My script calculate the difference in 2 time. Like this:
lasted = datetime.strptime(previous_time, FMT) - datetime.strptime(current_time, FMT)
Hope this fix your problem,
import datetime
start = datetime.datetime(2012,11,16,11,02,59)
end = datetime.datetime(2012,11,20,16,22,53)
delta = end-start
print ':'.join(str(delta).split(':')[:3])
In [29]: import datetime
In [30]: start = datetime.datetime(2012,11,16,11,02,59)
In [31]: end = datetime.datetime(2012,11,20,16,22,53)
In [32]: delta = end-start
In [33]: print ':'.join(str(delta).split(':')[:3])
4 days, 5:19:54