diff --git a/litellm/litellm_core_utils/llm_cost_calc/utils.py b/litellm/litellm_core_utils/llm_cost_calc/utils.py
index 9f28fe2b6fb..2527013e118 100644
--- a/litellm/litellm_core_utils/llm_cost_calc/utils.py
+++ b/litellm/litellm_core_utils/llm_cost_calc/utils.py
@@ -4,7 +4,7 @@
 import re
 from collections.abc import Mapping, Sequence
 from dataclasses import dataclass
-from datetime import date, datetime, timezone, tzinfo
+from datetime import date, datetime, time, timezone, tzinfo
 from types import MappingProxyType
 from typing import Final, Literal, TypedDict, cast
 from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
@@ -408,14 +408,7 @@ def _is_within_off_peak_window(off_peak_hours_utc: str | Sequence[str], current_
     """
     reference: Final = current_time if current_time is not None else current_billing_time()
     now: Final = (reference.astimezone(timezone.utc) if reference.tzinfo is not None else reference).time()
-    windows: Final = (off_peak_hours_utc,) if isinstance(off_peak_hours_utc, str) else off_peak_hours_utc
-    for window in windows:
-        try:
-            start_str, end_str = window.split("-")
-            start = datetime.strptime(start_str.strip(), "%H:%M").replace(tzinfo=timezone.utc).time()
-            end = datetime.strptime(end_str.strip(), "%H:%M").replace(tzinfo=timezone.utc).time()
-        except (ValueError, AttributeError):
-            continue
+    for start, end in _parse_windows(off_peak_hours_utc):
         if start < end:
             if start <= now < end:
                 return True
@@ -447,6 +440,21 @@ _WEEKDAY_NUMBERS: Final = MappingProxyType(
 )
 
 
+def _parse_window(window: object) -> tuple[time, time] | None:
+    try:
+        start_str, end_str = window.split("-")
+        start: Final = datetime.strptime(start_str.strip(), "%H:%M").replace(tzinfo=timezone.utc).time()
+        end: Final = datetime.strptime(end_str.strip(), "%H:%M").replace(tzinfo=timezone.utc).time()
+    except (ValueError, AttributeError):
+        return None
+    return (start, end)
+
+
+def _parse_windows(off_peak_hours_utc: str | Sequence[str]) -> tuple[tuple[time, time], ...]:
+    windows: Final = (off_peak_hours_utc,) if isinstance(off_peak_hours_utc, str) else off_peak_hours_utc
+    return tuple(parsed for window in windows if (parsed := _parse_window(window)) is not None)
+
+
 def _normalize_weekday(value: object) -> int | None:
     if isinstance(value, bool):
         return None
@@ -522,8 +530,8 @@ def _is_off_peak(off_peak: Mapping[str, object], current_time: datetime | None =
     hours apply only on its weekdays. A rule carrying override_dates applies only on those
     dates, read on the weekday_timezone calendar: on a listed date the matching rules alone
     decide (their weekdays are ignored, and the flat hours_utc and every other rule are
-    skipped), and on any other date the rule never applies (a malformed override_dates or
-    hours_utc disables the rule entirely).
+    skipped), and on any other date the rule never applies (a malformed override_dates, or an
+    hours_utc none of whose windows parse, disables the rule entirely).
     """
     reference: Final = current_time if current_time is not None else current_billing_time()
     reference_utc: Final = (
@@ -540,7 +548,7 @@ def _is_off_peak(off_peak: Mapping[str, object], current_time: datetime | None =
     override_rules: Final = tuple(
         rule
         for rule in rules
-        if _as_window_strings(rule.get("hours_utc")) and today in _as_dates(rule.get("override_dates"))
+        if _parse_windows(_as_window_strings(rule.get("hours_utc"))) and today in _as_dates(rule.get("override_dates"))
     )
     if override_rules:
         for rule in override_rules:
diff --git a/tests/test_litellm/litellm_core_utils/llm_cost_calc/test_llm_cost_calc_utils.py b/tests/test_litellm/litellm_core_utils/llm_cost_calc/test_llm_cost_calc_utils.py
index 385167e24fa..39a6ea684df 100644
--- a/tests/test_litellm/litellm_core_utils/llm_cost_calc/test_llm_cost_calc_utils.py
+++ b/tests/test_litellm/litellm_core_utils/llm_cost_calc/test_llm_cost_calc_utils.py
@@ -723,6 +723,9 @@ def test_is_off_peak_ignores_malformed_override_dates():
         ["2026-1-1"],
         ["2026-W01-4"],
         ["2026-01-1 "],
+        ["2026-02-30"],
+        ["2026-13-01"],
+        ["2026-01-011"],
     ):
         block = {"windows": peak_windows + [{"hours_utc": "00:00-00:00", "override_dates": bad}]}
         assert _is_off_peak(block, peak_instant) is False, (
@@ -740,11 +743,47 @@ def test_is_off_peak_override_rule_without_valid_hours_is_disabled():
         "windows": [
             {"override_dates": ["2026-03-03"], "hours_utc": 5},
             {"override_dates": ["2026-03-03"]},
+            {"override_dates": ["2026-03-03"], "hours_utc": "garbage"},
+            {"override_dates": ["2026-03-03"], "hours_utc": "25:00-26:00"},
+            {"override_dates": ["2026-03-03"], "hours_utc": ["4pm-midnight"]},
         ],
     }
     assert _is_off_peak(block, datetime(2026, 3, 3, 12, 0, tzinfo=timezone.utc)) is True
 
 
+def test_is_off_peak_override_rule_ignores_its_weekdays():
+    """On a date an override rule lists, its own weekdays field is ignored: a weekend-only
+    holiday rule still applies on the Thursday holiday."""
+    from datetime import datetime, timezone
+
+    block = {
+        "windows": [
+            {"hours_utc": ["00:00-01:00", "04:00-06:00", "10:00-00:00"], "weekdays": [1, 2, 3, 4, 5]},
+            {"hours_utc": "00:00-00:00", "weekdays": [6, 7], "override_dates": ["2026-01-01"]},
+        ],
+    }
+    holiday_thursday = datetime(2026, 1, 1, 2, 0, tzinfo=timezone.utc)
+    assert _is_off_peak(block, holiday_thursday) is True, (
+        f"{holiday_thursday.isoformat()} is a Thursday holiday billed off-peak all day"
+    )
+
+
+def test_is_off_peak_matching_override_rules_are_a_union():
+    """Every rule listing today's date applies: the date is off-peak inside any of their
+    windows, peak outside all of them."""
+    from datetime import datetime, timezone
+
+    block = {
+        "windows": [
+            {"override_dates": ["2026-03-03"], "hours_utc": "01:00-02:00"},
+            {"override_dates": ["2026-03-03"], "hours_utc": "12:00-13:00"},
+        ],
+    }
+    assert _is_off_peak(block, datetime(2026, 3, 3, 1, 30, tzinfo=timezone.utc)) is True
+    assert _is_off_peak(block, datetime(2026, 3, 3, 12, 30, tzinfo=timezone.utc)) is True
+    assert _is_off_peak(block, datetime(2026, 3, 3, 5, 0, tzinfo=timezone.utc)) is False
+
+
 def test_is_off_peak_disables_rules_with_partially_malformed_override_dates():
     """One bad entry disables the whole override_dates list: a rule whose dates do not all
     parse never applies on any date, so the flat hours decide alone."""
@@ -803,6 +842,35 @@ def test_override_dates_use_weekday_timezone_calendar_on_shipped_deepseek_rows()
     ]
     assert not drifted, f"off_peak schedule drift on {drifted}"
 
+    from datetime import date, timedelta
+
+    windows: Final = block["windows"]
+    assert windows[:2] == [
+        {"hours_utc": ["00:00-01:00", "04:00-06:00", "10:00-00:00"], "weekdays": [1, 2, 3, 4, 5]},
+        {"hours_utc": "00:00-00:00", "weekdays": [6, 7]},
+    ]
+    holidays: Final = {
+        (start + timedelta(days=offset)).isoformat()
+        for start, days in (
+            (date(2026, 1, 1), 3),
+            (date(2026, 2, 15), 9),
+            (date(2026, 4, 4), 3),
+            (date(2026, 5, 1), 5),
+            (date(2026, 6, 19), 3),
+            (date(2026, 9, 25), 3),
+            (date(2026, 10, 1), 7),
+        )
+        for offset in range(days)
+    }
+    workdays: Final = {"2026-01-04", "2026-02-14", "2026-02-28", "2026-05-09", "2026-09-20", "2026-10-10"}
+    holiday_rule, workday_rule = windows[2], windows[3]
+    assert holiday_rule["hours_utc"] == "00:00-00:00"
+    assert set(holiday_rule["override_dates"]) == holidays
+    assert workday_rule["hours_utc"] == windows[0]["hours_utc"]
+    assert set(workday_rule["override_dates"]) == workdays
+    assert holidays.isdisjoint(workdays)
+    assert all(date.fromisoformat(day).isoweekday() in (6, 7) for day in workdays)
+
     shanghai_make_up_sunday = datetime(2026, 1, 3, 17, 0, tzinfo=timezone.utc)
     make_up_sunday_peak = datetime(2026, 1, 4, 2, 0, tzinfo=timezone.utc)
     plain_sunday = datetime(2026, 1, 11, 2, 0, tzinfo=timezone.utc)
diff --git a/tests/test_litellm/test_model_prices_schema.py b/tests/test_litellm/test_model_prices_schema.py
index 2437a8b6700..329d62b4efe 100644
--- a/tests/test_litellm/test_model_prices_schema.py
+++ b/tests/test_litellm/test_model_prices_schema.py
@@ -392,7 +392,11 @@ def deepseek_off_peak_drift(entry: Mapping[str, object]) -> str | None:
     windows: Final = tuple(block.get("windows", ()))
     if windows[: len(DEEPSEEK_OFF_PEAK_WINDOWS)] != DEEPSEEK_OFF_PEAK_WINDOWS:
         return f"windows={block.get('windows')}"
-    if not all("override_dates" in rule for rule in windows[len(DEEPSEEK_OFF_PEAK_WINDOWS) :]):
+    if not all(
+        "override_dates" in rule
+        and rule.get("hours_utc") in ("00:00-00:00", DEEPSEEK_OFF_PEAK_WINDOWS[0]["hours_utc"])
+        for rule in windows[len(DEEPSEEK_OFF_PEAK_WINDOWS) :]
+    ):
         return f"windows={block.get('windows')}"
     halved: Final = {rate: block.get(rate) for rate in DEEPSEEK_HALVED_RATES}
     expected: Final = {rate: float(str(entry[rate])) / 2 for rate in DEEPSEEK_HALVED_RATES}
diff --git a/tests/test_litellm/test_utils.py b/tests/test_litellm/test_utils.py
index 46ae7fd1e79..e3a5820396b 100644
--- a/tests/test_litellm/test_utils.py
+++ b/tests/test_litellm/test_utils.py
@@ -1057,7 +1057,11 @@ def test_aaamodel_prices_and_context_window_json_is_valid():
                                         "type": "array",
                                         "items": {"oneOf": [{"type": "integer"}, {"type": "string"}]},
                                     },
-                                    "override_dates": {"type": "array", "items": {"type": "string"}},
+                                    "override_dates": {
+                                        "type": "array",
+                                        "minItems": 1,
+                                        "items": {"type": "string", "pattern": "^\\d{4}-\\d{2}-\\d{2}$"},
+                                    },
                                 },
                                 "required": ["hours_utc"],
                                 "additionalProperties": False,