diff --git a/search/retrieval.py b/search/retrieval.py
index bdebd06..c6208d3 100644
--- a/search/retrieval.py
+++ b/search/retrieval.py
@@ -1,3 +1,4 @@
+from datetime import datetime
 from typing import Any
 
 from qdrant_client import AsyncQdrantClient, models
@@ -14,6 +15,13 @@ from config import (
 from schemas import Question, SparseVector
 
 
+def _iso_to_unix(s: str) -> float:
+    try:
+        return datetime.fromisoformat(s.replace("Z", "+00:00")).timestamp()
+    except (ValueError, AttributeError):
+        return 0.0
+
+
 def _build_filter(question: Question) -> models.Filter | None:
     must_conditions: list[models.Condition] = []
 
@@ -22,8 +30,8 @@ def _build_filter(question: Question) -> models.Filter | None:
             models.FieldCondition(
                 key="metadata.start",
                 range=models.Range(
-                    gte=question.date_range.from_,
-                    lte=question.date_range.to,
+                    gte=_iso_to_unix(question.date_range.from_),
+                    lte=_iso_to_unix(question.date_range.to),
                 ),
             )
         )