Excel 2007 Data Validation Query - sum of two cells less than a set number

[KJ2607]

Hello Everyone!

I am wanting to create a validation rule so when two cells are added the together the answer must be less than or equal to 14:00 - otherwise a message box will appear

So for example if H7+I7 gives an answer of 13:00 in J7, that's OK, but if the answer is 15:00, the error box will appear. I know that data validation doesnt work on a cell that already has a formula so I'm hoping to use K7 for the Validation and then hide the column

I'm sure there's a simple answer for this but I've clearly being staring at this for too long now

Thanks in Advance