If you enter 150 into a number field, a calculation can turn this into time with this expression:
NumberField * 60 //converts minutes into seconds.
If you specify Time as the return type for your calculation field or use a field of type Time with this expression as the auto-entered calculation, you'll be able to enter the time in minutes, but express it and use it as Time.
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That nailed it—thank you, and now your help has uncovered a series of other calculations that will now make life easier.