How do I convert game time (seconds) to int64 for Game Centre?

Yes, the first screenshot is me submitting the score to game centre, and the second shot is what the score looks like in game centre.

its the mobile version of this game http://www.stencyl.com/game/play/27884

Never been into GameCenter; is it possible that when setting up the game you can set the field to assume time?

Yeah exactly, see attached

Yes. The confusing part (for me anyway) is because I'm submitting a time rather than a score, this has to be done via a 64bit signed integer which is then converted back into a time at the other end.

Are you sure about this 64bit thing? I just submitted my time attribute and it worked.

I think I've totally been over thinking this one!!  I've attached a screenshot of where it says about this but i think it's probably just saying don't try and submit your time as "00:02:22" or "00.02.22" or any other weird way, but just submit it in seconds as a standard integer, i.e 142

Duh!