On the Extra Life page it says "Starting at 8am in you local timezone. Can we start whenever for example when the US start so we can play together with them?

That's a good question.
I don't think it matters. Because they were saying as long as you do 24 hours it's all good. If you do two 12 hour shifts, or 12 two hour shifts, ect. As long as you do your 24 hours it should be okay.
But I'm new to this. So for an official ruling you should email Doc thru SG. He'll be able to answer this question correctly.:thumbsup:

I was more wondering whether us in the UK and start with the US so its more of a community eveny

You can play whenever you want. They set dates and times to encourage people to be on at those times.

You can start whenever! The main goal is just to do the 24 hours! However, you are welcome to take breaks and do it however works best for you!

What time in GMT is when the majority of US start ?