how to convert the time stmp to hour, min and sec in PHP

//convert to min and sec
$convert_min = $diff/60;
$convert_sec = $diff % 60;//seconds

//convert to hours and min
$convert_hr = floor($convert_min/60);//hours
$remainder = floor($convert_min % 60);//minutes
 
$total_visit =  $convert_hr.":".$remainder;