Extended Template Tag initially created by Dan Ward (http://d-w.me): https://djangosnippets.org/snippets/1398/
The default setting has been renamed to normal, output stays the same. If you have used the old tag with ':short' you have to remove or rename it to ':normal' for the same ouput!
As an example, given the duration 84658:
Short: 23:30:58 Normal (default): 23 hrs 30 mins 58 secs Long: 23 hours, 30 minutes and 58 seconds