5 hours is unfair if the thread goes up at 11pm for a 4am GMT deadline. I think if the thread is posted between 11pm and 3am GMT it should be at least 9 hours before the deadline but if it's any other time then 6 hours is plenty.

I disagree. The WHOLE argument is entirely based upon people's sleeping patterns (or your assumption of them). Either you have ONE fixed limit (i.e. 5 hours, 9 hours) or you have none at all. The entire point of the game is to get your predictions in on time. You can't decide amongst yourselves each time a thread is posted up whether it should count or not.
Personally, unless it's been obviously missed by everyone for like OOP + 12 hours or something silly like that, then every thread should count. I'm perfectly happy for this one to count, but only cause I think the rule is rubbish in the way it has been written up.