My choice will be to convert date1 and date2 into timestamp.
Well, u can separate year, month, day, hour, min, second using explode()
U can use mktime() to create the timestamp
Then... just substract $date2-$date1 (assuming $date2 is greater than $date1)... you'll get the diff in seconds... to get it in minutes... divide by 60. 🙂
HTH.