If you are using the php function strtotime() and find that the resulting timestamp is not correct then here is the solution

We were writing a simple function that needed the date string in the format "d-m-Y H:i:s" to be converted to a timestamp for processing. For some reason the resulting output was always an hour out. The problem was that the timezone was not specified in the date string.

Bad strtotime input:

strtotime('20-07-1988 12:00:00') 

Correct string to time input

strtotime('20-07-1988 12:00:00 GMT')  

A simple issue with a simple resolution but one that may not be obvious to spot by using the php strtotime api alone.