The request was to convert 3.50 to 3:30, not 3.30 to 3:30.
Then introduce a code that accepts only time as input(Error message for decimal and text input(Unfortunately, there is not.
The simple solution is to change the user, not the code. Enter all times in a consistent format and your problem is solved.
Is it possible to identify the entry format?Times are decimals, so that is not possible either.
12:00 = 0.5 days, 3.5 days = 84:00 hours, there is no way to identify which was entered.