[php] Strtotime() doesn't work with dd/mm/YYYY format

From the STRTOTIME writeup Note:

Dates in the m/d/y or d-m-y formats are disambiguated by looking at the separator between the various components: if the separator is a slash (/), then the American m/d/y is assumed; whereas if the separator is a dash (-) or a dot (.), then the European d-m-y format is assumed.

It is as simple as that.