from datetime import datetime
start_date = 'Sun Sep 16 16:05:15 +0000 2012'
end_date = 'Sun Sep 17 23:55:20 +0000 2012'

def __datetime(date_str):
    return datetime.strptime(date_str, '%a %b %d %H:%M:%S +0000 %Y')
start = __datetime(start_date)
end = __datetime(end_date)
delta = end - start
print(delta)
print(delta.total_seconds())
Python вычитает две строки даты