Having an issue with how to calculate a time differance

[jabourgeois1]

At this point my data base is working from what I can tell. The issue I am having is when you log in as student (Test # is 111111111), set your CLOCKIN time, then CLOCKOUT 25 min later. Great! The next clockin time has to be a minimum for 4 hours later. This is where I am having trouble. I know the check needs to be in the onclick event for the clock in but I can't figure out where in the code to put it and I have tried using datediff ("n" [timeout], now()) <=240. I am thinking that I am not getting the time from the last clockout from that record to calculate the difference.



for those that need to-- the line at the top of the "hours page" is a button for the admin side Login in is: (admin/admin, director/director, or staff/staff)
you have to input a student before you are able to log in as that student, basically the first line of the record once you are in the admin side
I have already input student 111111111.

the other two buttons (employee & patron) are part of an on going project