PHP date time to Unix time Stamp

How can I convert string "M-d-Y::H:i:s" to unix timestamp in php. I just realized manipulating date and time must be the most time consuming entity in any programming language.

Trivial Question: Why do you think there isn't any universal date time format. Why are there so many variations of same data? AArrhh.

Copyright License：
Author:「srijan」,Reproduced under the CC 4.0 BY-SA copyright license with link to original source & disclaimer.
Link to：https://stackoverflow.com/questions/11544590/php-date-time-to-unix-time-stamp