Add values of a (Text - Multiple Choice)

I have two fields (Text - Multiple Choice) called (Entry Time) and (Exit Time) that keep track of the hours of the day example:

12:00
01:00
02:00
03:00 etc..

I want the values selected in each of the fields to be summed in another formula field, how do I make it so that from a text field I can choose the values as a number to be able to sum them.

Currently I have a Formula-Duration type field, but it doesn't work because the field is text.

Any ideas?


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Jaime Fonseca
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