Time Interval support in Templates

I would like to add template functions and filters:

   sec_to_time_interval()         125 ->  "02:05"
   time_interval_to_sec()        "1:01:01"  ->    3661

I have already added these for my own use. If others are interested let me know and I will try to work through the submission process.

For my automation I use text selector witch will take:
YYY:DDD:HH:MM:SS (all fields are optional except SS)
I have thought about a selector (similar to the time selector).

Let me know what you think!