You can create a microflow which calculates the time between both dateTime elements.
On this page you can read more about the between date function.
I think would calculate the minutes between and determine the full hours and leftover minutes to get a work time 7h 34min. Or use hours between and take the rest value (after the decimal) to recalculate it to minutes. Say 0.5 hour should be translated into 30 min.
You can use the "minutesbetween" function in Mendix, see the referrence guide for more info: https://world.mendix.com/display/refguide6/Between+date+function+calls