That's pretty weird. But I think there are two ways you could handle it, the first of which is likely the better way.
1. You could use the FormatDateTime() function like this in your Expression:
FormatDateTime([Hour To], "HH:mm")
Then, valid values would be like "13:00" or "1:00 PM", both of which would result in the value "13:00".
2. You could change the input to be Text and then just do a validation on the inputted values but then use values in [Hour To] without any kind of conversion to ensure the exact values are used.
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Dave Morris
Cano Ai
Atlanta, GA
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Dave Morris, 3Ci at Southern Company