Ahh... I think I understand better.
Personally, I don't like using the colon for time either. Times are difficult to enter using the number pad, because there isn't any colon on the number pad.
I wouldn't mind hitting a decimal for a min:sec separator, because it is on the number pad. But that can be confused with normal numbers. However, it would be nice if the parsing object/system automatically converted 10.20 to 10:20 if it is in a time field.
The ultimate solution is to go to metric time. ;)
http://zapatopi.net/metrictime/