int strtotime ( string time [, int now] ) converts strings to a timestamp

 
<?
    print strtotime("22nd December 1979");
    print strtotime("22 Dec. 1979 17:30");
    print strtotime("1979/12/22");
?>

1.	Calculating a date interval with strtotime()
2.	Checking a date range
3.	Using strtotime()
4.	Using strtotime() with a starting epoch timestamp
5.	Find the First monday on or after November 1, 2008
6.	Find weekday
7.	Finding the Date for a Weekday
8.	Getting the Day and Week of the Year
9.	If PHP is unable to convert your string into a timestamp, it will return -1.
10.	Obtaining the Difference Between Two Dates
11.	Subtracts a year from a given timestamp

int strtotime ( string time [, int now] ) converts strings to a timestamp : strtotime « String « PHP