If you only want particular PHP scripts (not a cgi scripts) to use a specific timezone, set the timezone environmental variable in your PHP code like so:
echo "Original Time: ". date("h:i:s")."\n";
echo "New Time: ". date("h:i:s")."\n";
If you put the line putenv("TZ=US/Eastern"); in a file that is
include()'ed by all your other PHP scripts, then all your PHP scripts will use that timezone.
A list of timezones to choose from, other than "US/Eastern" for your putenv() is here: