Below is the formula that I would like to use with only one major modification Where "zeros" should show too. Not on empty cells, only if it is input.
The input reprsents time in 24 hour format. Such as 1300, (hrs), 2300, 0600, 0000 (instead of 2400). When I input any number that is preceded by a "0", (I.e. 0700, 0230, 0000,), I receive an error message. all other numbers not preceded by "0", works fine.
Any help on modifiying the formula to allow the cell to accept numbers preceded by "0", is greatly appreciated.


Here's the formula:

=AND(ISNUMBER(A1),LEN(A1)=4)

Thank you.