stock-time.py: use python3 shebang and return start time from get_start

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

stock-time.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python3.5
+#!/usr/bin/python3
 """Calculate the stocking speed of employees"""
 from datetime import timedelta
 
@@ -21,7 +21,7 @@ class Person():
     def get_start(self):
         """Gets start_time""" #store the delta start time here
 
-        return self
+        return self.start_time
 
     def get_end(self):
         """get end time"""