date conversion and calculation problem...

Hello, I have 2 date string like this $t1 = "2001-11-12 17:30:10"; $t2 = "2001-11-12 17:15:32"; I need to substracts the number of seconds from $t2 from $t1 (because after I have another script thats converts the number of seconds to minutes, hours or days if necessary) I tried: (but it does not give me something rigth) $t1 = explode( " ", $t1 ); $t2 = explode( " ", $t2 ); // now $t1[0] contains date $t1[1] contains hours $arr_date1 = explode( "-", $t1[0] ); $arr_date2 = explode( "-", $t2[0] ); $arr_time1 = explode( ":", $t1[1] ); $arr_time2 = explode( ":", $t2[1] ); // now $arr_time1[0] contains the hour, $arr_time1[1] contains minute, $arr_time1[2] contains second $t1 = mktime( $arr_time1[0], $arr_time1[1], $arr_time1[2], $arr_date1[1], $arr_date1[1], $arr_date1[0] ); $t2 = mktime( $arr_time2[0], $arr_time2[1], $arr_time2[2], $arr_date2[1], $arr_date2[2], $arr_date2[0] ); print "<br>$t2 - $t1 = ". ( $t2 - $t1); hope you can help me, py