how to validate 12 hr and 24 hr format in one textbox

i have to validate a time in a textbox  in 12 hr and 24 hr format...for that i have two checkboxes like 12 hr and 24 hr if i checked 12 hr then that textbox should accept only 12 hr format if i checked 24 hr only 24 hr format should accept how to do this???

 

am sharing what i tried...

 

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