Time Duration on Forms

Is there any way to have a field on a form where it adds multiple time duration fields together? For example: I'd like to be able to do the following:

Field: Duration #1 (data manually entered on form by user)

Field: Duration #2 (data manually entered on form by user)

Field: Duration #3 (data manually entered on form by user)

I'd like a Read-Only 'running total' field that adds all of the data in the above fields to show the total duration spent on the task. I'm not interested in any graphs or widget, etc. I just want raw data added together for user tracking on the form itself.