Excel 2007 VBA Message Box with criteria

Hi I am VERY new to VBA and am starting to get confused!

I have a spreadsheet that monitors employees rest periods between shifts across a number of weeks I've started writing a very basic piece of code so if the employee has less than 12 hours rest, a message box will appear with a warning:

So far this is what I've done:

Sub RestHours()

If Range("I7") < #12:00:00 PM# Then

MsgBox "Candidate has had less than 12 hours rest since last shift worked. Please find another candidate to work this shift", vbOKOnly, "Unable to Use Candidate!"


Now this does work if I run the macro and then enter the data into cell I7, however I'm now stumped - How can I make it so that this message box pops up automatically when the data is entered into the cell without me have to go in and run the macro?

I also need the macro to run all the way down the I column (I7:I100) and across other columns which will eventually contain the same data i.e. M7:M100, Q7:Q100, all the way across to AT7:AT100? If its any help the columns have the same title (Total Rest Hours)

Hi Xlbiznes,

Thanks for this - I dont quite understand how to use this piece of code - do I need to put the piece I had already written in somewhere? I think at the moment I need things spelling out to me very simply