(3.0.12 - 3.0.18 only, PHP 4 >= 4.0.0)strtotime -- Parse about any English textual datetime description into a UNIX timestamp
The function expects to be given a string containing an English date format and will try to parse that format into a UNIX timestamp relative to the timestamp given in now, or the current time if none is supplied. Upon failure, -1 is returned.
Because strtotime() behaves according to GNU date syntax, have a look at the GNU manual page titled Date Input Formats. Described there is valid syntax for the time parameter.
Example 1. strtotime() examples
Note: The valid range of a timestamp is typically from Fri, 13 Dec 1901 20:45:54 GMT to Tue, 19 Jan 2038 03:14:07 GMT. (These are the dates that correspond to the minimum and maximum values for a 32-bit signed integer.)