Idea on how to create a list of hours and add them up?

I want to have two fields (Time In and Time Out) with all the hours of the day, e.g.
12:00
01:00
02:00
03:00 etc

But I can't find a way to add in another field the chosen option of Time In and Time Out.

What field can I use to recognize the values entered in Text - Multiple Choice) as a number and be able to add them.

I have tried with Numeric-Raiting and also not, it only adds me in a normal way not as hours.

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Jaime Fonseca
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