$t1=mktime(0,0,0,1,1,1970): -3600
$t2=mktime(23,59,59,1,31,2013): 1359673199
$t1=gmmktime(0,0,0,1,1,1970): 0
$t2=gmmktime(23,59,59,1,31,2013): 1359676799

date_default_timezone_set("UTC")
$t1=mktime(0,0,0,1,1,1970): 0
$t2=mktime(23,59,59,1,31,2013): 1359676799
$t1=gmmktime(0,0,0,1,1,1970): 0
$t2=gmmktime(23,59,59,1,31,2013): 1359676799

date_default_timezone_set("America/Los_Angeles")
$t1=mktime(0,0,0,1,1,1970): 28800
$t2=mktime(23,59,59,1,31,2013): 1359705599
$t1=gmmktime(0,0,0,1,1,1970): 0
$t2=gmmktime(23,59,59,1,31,2013): 1359676799

date_default_timezone_set("Europe/Budapest")
$t1=mktime(0,0,0,1,1,1970): -3600
$t2=mktime(23,59,59,1,31,2013): 1359673199
$t1=gmmktime(0,0,0,1,1,1970): 0
$t2=gmmktime(23,59,59,1,31,2013): 1359676799