Help with data in seconds for time difference calculation

[Penny Cross]

Dear REDCap friends

I am trying to calculate the time difference for 2 fields in timing children doing particular tasks using the mobile app on iPads/tablets.

The input times are measured using the REDCap “stopwatch” function for “start” and “end” times for each task, using a validation of Datetime w/seconds (D-M-Y H:M:S). The exports of the data show the data for both the start and end times accurate to whole seconds. The time difference is then calculated using this calculation:

 datediff([ms_stug_1st_try_start], [ms_stug_1st_try_end], "s")

However sometimes the times need to be more accurate than just whole seconds. Is there a way to display the time and the time difference in smaller units than seconds or displaying the time difference in seconds but with perhaps 2 decimal points similar to a physical stopwatch? 

Thanks in advance for your help.

Penny Cross