03-01-2014 01:00 am
is ambiguous. Is it March 1st? Or April 3rd? From the manual:
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.
To avoid potential ambiguity, it's best to use ISO 8601 (YYYY-MM-DD) dates or DateTime::createFromFormat() when possible.
$date = DateTime::createFromFormat('m-d-Y h:i a', '03-01-2014 01:00 am');
echo $date->format('Y-m-d H:i:s');