Mid may is a lovely time to visit the towers, between the two bank holidays, and before the students finish and the school trips begin.
Midweek queues for the bigger rides at this time of year are usually around the fifteen to thirty minute mark,
with the Smiler around an hour or so.
Early hours are often walk on until noon.
My favourite time of year for a visit.
I never go on a weekend, but I imagine the queues would double at that time of year.
May the 4th, as well as being Star Wars Day(!), is the bank holiday, so would probably be busy, but this is never guaranteed, as some bank holidays have been known to be quiet.
I would go midweek if I were you.