$given = 685;
/*
* In case $given == 86400, gmdate( "H" ) will convert it into '00' i.e. midnight.
* We would need to take this into consideration, and so we will first
* check the ratio of the seconds i.e. $given:$number_of_sec_in_a_day
* and then after multiplying it by the number of hours in a day (24), we
* will just use "floor" to get the number of hours as the rest would
* be the minutes and seconds anyways.
*
* We can also have minutes and seconds combined in one variable,
* e.g. $min_sec = gmdate( "i:s", $given );
* But for versatility sake, I have taken them separately.
*/
$hours = ( $given > 86399 ) ? '0'.floor( ( $given / 86400 ) * 24 )-gmdate( "H", $given ) : gmdate("H", $given );
$min = gmdate( "i", $given );
$sec = gmdate( "s", $given );
echo $formatted_string = $hours.':'.$min.':'.$sec;