What?
This is intended for activity/session durations and although I usually get MySQL to do the date/time calculations, there are times when we have to do with PHP. This is the shortest way I know to properly convert seconds into total hours, minutes and seconds (taking into account regional settings and without using a date function).

How?
$total_time =intval(intval($total_seconds)/ 3600).":";
$total_time.=str_pad(intval(($total_seconds/60)%60),2,"0",STR_PAD_LEFT).":";
$total_time.=str_pad(intval($total_seconds%60),2,"0",STR_PAD_LEFT);

// yields
// 82800  = 23:00:00
// 108000 = 30:00:00
On one line: 
$total_time=intval(intval($total_seconds)/ 3600).":".str_pad(intval(($total_seconds/60)%60),2,"0",STR_PAD_LEFT).":".str_pad(intval($total_seconds%60),2,"0",STR_PAD_LEFT);