Haven't a clue off the top of my head about bank holidays, but normally on weekends, queues can soar as high as 2 hours - and you think you'll survive two hours in what's practically a PRISON with the constant "HA-HA-HA...HA-HA-HA...HA-HA-HA-HA-HA-HA-HA" blasting away in the background!
What you DO need to take into account TPF is that Towers is the only remaining Merlin park (I think) with Single Rider. Use this to your advantage!