Obtain a result from the diference between 2 timestamps - forum topic by awesome

Hi everybody,
 
I want to obtain the diference between to timestamp fields
Example:
Timestamp field 1: '12:49:00'
Timestamp Field 2: '12:51:15'
Result must be: '00:02:15' (the time elapsed between the field1 and field2)
 
How can obtain this result?
Thanks in advance for your support.