Hey... i have searched for the answer but cannot find what i am looking for so i am turning to you people, hoping i can find out what i need.

Anyway.... I have made a forum and now i am looking to add a feature that lists all the users online at the present time. I am going to acheive this by checking if the 'last active time' is less than 15minutes old. If it is then the user will be classed as online and vice versa.

I just haven't got the foggiest on how to compare the last active time and the current time, and then see if the difference is less than 15 minutes.

Can anybody please help me?? Cheers, BIOSTALL