diff --git a/make_graphs.py b/make_graphs.py
index 1847ff3..d7924da 100644
--- a/make_graphs.py
+++ b/make_graphs.py
@@ -208,7 +208,7 @@ class InputAnalyzer(CsvAnalyzer):
                 if sec not in responsepersec:
                     responsepersec[sec] = []
                 else:
-                    firetime = date_time_obj = datetime.datetime.strptime(sec, '%Y-%m-%dT%H:%M:%S')
+                    firetime = datetime.datetime.strptime(sec, '%Y-%m-%dT%H:%M:%S')
                     responsearrivetime = datetime.datetime.strptime(item['response_arrive_time'],
                                                                     "%Y-%m-%dT%H:%M:%S.%f")
                     latency = responsearrivetime - firetime