Well obviously going on a Saturday there is more chance of queues than on a weekday but its always, where ever you go and whatever day, its going to be hit or miss. I dont really think you need to wait till after the summer, just try and go in the week, because obviously schools have just gone back, so in the week would be better. Also, try and use tesco club card vouchers (if you have a clubcard) or kellogs vouchers which will give you a discount to get in. In terms of rides being closed, Im not sure, but some of the major rides occasionally dont operate till after 12am, so bare that in mind.