diff --git a/skillopt_sleep/cycle.py b/skillopt_sleep/cycle.py
index e66f436..9375784 100644
--- a/skillopt_sleep/cycle.py
+++ b/skillopt_sleep/cycle.py
@@ -150,7 +150,8 @@ def run_sleep_cycle(
             lookback_hours = cfg.get("lookback_hours", 72)
             if lookback_hours and lookback_hours > 0:
                 import time
-                cutoff = time.time() - lookback_hours * 3600
+                ref_time = clock if clock is not None else time.time()
+                cutoff = ref_time - lookback_hours * 3600
                 since = _now_iso(cutoff)
         max_tasks = cfg.get("max_tasks_per_night", 40)
         max_sessions = cfg.get("max_sessions_per_night", 0) or max_tasks * 3
diff --git a/skillopt_sleep/harvest.py b/skillopt_sleep/harvest.py
index 3645d3f..84446f8 100644
--- a/skillopt_sleep/harvest.py
+++ b/skillopt_sleep/harvest.py
@@ -294,7 +294,9 @@ def harvest(
         if not _project_matches(d.project or "", scope, invoked_project):
             continue
         if since_iso and d.ended_at and d.ended_at < since_iso:
-            continue
+            # Files are sorted newest-first by mtime; once we see one that
+            # is older than the cutoff, all remaining files are older too.
+            break
         digests.append(d)
         if limit and len(digests) >= limit:
             break