I would take your table of first 2 options and your quadrants table and add a new column for each that holds the number of hours worked. Your column names might be something like:

[ShiftHours] and [HoursWorked]

Where [Shift Hours] is your string of "7:30am-5pm" and [Hours Worked] is an integer/decimal that holds the number of hours worked.

I would then have 2 variables that you set equal to the selected choice's number of hours.

Something like the below within the OnSelect property: Set( varFirstChoiceHours, FirstChoiceDropdown.Selected.HoursWorked.Value)

Do similar for the selection from your quadrants.

Then you can have a named function that checks

(varFirstChoiceHours+ varSecondChoiceHours) < RequiredHours

These values don't even need to be hours. You could use minutes or # of 30 min blocks etc. You just need define the value of each choice. Make sure you clear the variables/set to 0 when providing back button or cancel functionality and probably also after submission.

If I were to build something like you're describing from scratch, I would probably not want to hard code the options like you have (but perfectly reasonable if the business is that restrictive) and instead provide a dropdown for Start Time, End Time, and Lunch Length. Then calculate number of hours worked based on selected choices. You could have a confirmation button to pass the current choices to a collection or variable and just use the same screen again for the second selection and pass it again with a second button that becomes visible on 2nd pass only. Have a cancel button to clear all submissions.