$MatchStartTime = $MatchDate . " " . $_POST["MatchStartTime"];
'2007-01-01 10:30:00' ($MatchStartTime)
What I need to do is take $MatchStartTime and minus 5 hours off it. So in the above example it would be '2007-01-01 5:30:00' or if someone specifies '2007-01-01 22:30:00' the system would calculate it as '2007-01-01 17:30:00', etc, etc.
How could I do this? The field in the database is a DateTime field.