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// microtime(true) returns the unix timestamp plus milliseconds as a float
$starttime = microtime(true);
/* do stuff here */
$endtime = microtime(true);
$timediff = $endtime - $starttime;
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$start = new DateTime('2022-10-01 10:00:00');
$now = new DateTime();
$interval = $now->diff($start);
echo $interval->format('%y years %m months %d days %h hours %i minutes %s seconds');