Tim,
It's a 24 hour deal (not 12) 
any time between 9am UK time on Friday, June 18 and 9am Saturday, June 19
and if you're 9 hours ahead of UK, that's from 6pm Friday to 6pm Saturday
OK, well I was wrong by 24 hours!

Typical ... I'm rubbish at working out stuff like that.
Good-o, so I know what I'll be doing later this evening.

Thanks morganllan. If I'd relied on myself I'd be most disappointed this time tomorrow ...

I believe they changed it because the site couldn't cope the first time. Morganllan, do you know if you have to use the full 90 minutes in one hit, or can you do some now and some later?