If you want to create a audio/video duration string like YouTube, etc. you can do:
($seconds >= 60) ? ltrim(gmdate("H:i:s", $seconds), ":0") : gmdate("0:s", $seconds)
Will return strings like:
55.55 => '0:55'
100 => '1:40'
Probably won't work well for time >= 24 hours.