Easy,
First: use mktime() to get the start date into seconds so we can do some math.
Second: get the current number of seconds since like Jan 1. 1971 or thereabouts, (ie just use time() function)
Third: subtract the time() - start date and you have the number of seconds elapsed.
Fourth: Take your result divided by (606024) to get the number of hours passed.
I've done everything except write the script for ya! It's not a difficult one to figure out.
Hic