Here are the rules explained nicely: https://www.gov.uk/apply-free-childcare-if-youre-working So you can get funded hours from September, and you apply during the previous term - best to check with your nursery about deadlines :)
You can apply for it now so it's all set up, but yiu need to renew your account every 3 months I think, or you will need to renew at least once before you go the hours anyway but just apply. I have done mine and go back to work in May, but I don't get hours until September. I renew in may, and then might have to renew it again before September x
September 1st
Apply may/June time as funding won't start until September. I emailed my nursery and got them to help me with it all ad I got confused with dates (and I've already got one at nursery so dread to think how confusing it must be if you're new to it all)
You can start the application now but the earliest you can submit is 31 days prior to your return to work date.
It's the term after they turn 9 months. So you can claim from September x