diff --git a/backfiller/backfiller/main.py b/backfiller/backfiller/main.py
index 40e9b38..c66a78d 100644
--- a/backfiller/backfiller/main.py
+++ b/backfiller/backfiller/main.py
@@ -142,14 +142,18 @@ def list_hours(node, stream, variants, start=None):
 	ordered from newest to oldest.
 	
 	Keyword arguments:
-	start -- Only return hours after this time. If None (default), all hours are
-	returned."""
+	start -- If a datetime return hours after that datetime. If a number,
+	return hours more recent than that number of hours ago. If None (default),
+	all hours are returned."""
 
 	hour_lists = [list_remote_hours(node, stream, variant) for variant in variants]
 	hours = list(set().union(*hour_lists))
 	hours.sort(reverse=True) #latest hour first
 
+
 	if start is not None:
+		if not isinstance(start, datetime.datetime):
+			start = datetime.datetime.utcnow() - datetime.timedelta(hours=start)
 		hours = [hour for hour in hours if datetime.datetime.strptime(hour, HOUR_FMT) < start]
 	
 	return hours
@@ -329,8 +333,12 @@ def main(base_dir='.', stream='', variants='', metrics_port=8002,
 
 	variants = variants.split(',') if variants else []
 	static_nodes = static_nodes.split(',') if static_nodes else []
+
 	if start is not None:
-		start = dateutil.parser.parse(start)
+		try:
+			start = float(start)
+		except ValueError:
+			start = dateutil.parser.parse(start)
 
 	manager = BackfillerManager(base_dir, stream, variants, static_nodes, start, run_once)
 	gevent.signal(signal.SIGTERM, manager.stop)