It is easy to fill a day there so you’ll be fine. If you can squeeze in an extra half day there is Splash Landings there – a water park too which is supposed to be very good – i’ve not been but the wife has taken the kids there a few times during holidays and they love it. There is a hotel on site, which I imagine is not too cheap, but if you stay there you might get deals on entrance, which might make the total package cost affordable, and it might be the case that in order to entice people there after the recent unfortunate accident there could be some deals to be had. Worth checking out.
Also if you have any Tesco vouchers you can use them towards entrance tickets.
I think there is a campsite nearby too if that’s your bag.
During term time weekday’s are best, but obviously weekends and school holidays will be busy. You’re looking at 45 mins to an hour or maybe more queuing for the bigger rides.