diff --git a/services/aggregation/pattern_matcher.py b/services/aggregation/pattern_matcher.py
index d04d6d2..c3af73f 100644
--- a/services/aggregation/pattern_matcher.py
+++ b/services/aggregation/pattern_matcher.py
@@ -209,10 +209,10 @@ ORDER BY md.published_at DESC
 # Horizon → interval mapping
 # ---------------------------------------------------------------------------
 
-_HORIZON_INTERVALS: dict[str, str] = {
-    "1d": "1 day",
-    "7d": "7 days",
-    "30d": "30 days",
+_HORIZON_INTERVALS: dict[str, timedelta] = {
+    "1d": timedelta(days=1),
+    "7d": timedelta(days=7),
+    "30d": timedelta(days=30),
 }