coopster - 9:40 pm on Jan 20, 2013 (gmt 0)
From the manual page: [php.net...]
Each parameter of this function uses the default time zone unless a time zone is specified in that parameter. Be careful not to use different time zones in each parameter unless that is intended. See date_default_timezone_get() on the various ways to define the default time zone.
You are likely going to need to be more specific with your time string. See the Date and Time Format page for more information: