mktime() - Get Unix timestamp for a date
echo mktime(23, 24, 0, 11, 3, 2009);
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To handle AM/PM just add 12 to hours if PM.
mktime($isAM ? $hrs : ($hrs + 12), $mins, $secs, $m, $d, $y);
Alternatively you could use strtotime():
strtotime() - Parse about any English textual datetime description into a Unix timestamp
echo strtotime("2009-11-03 11:24:00PM");
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