A couple of hours is probably about right. On a really windy day you could get dry rock a bit sooner.
Loads of cool problems to go at, and it always feels different because the pebble levels shift about (bit like Angel Bay). There is an excellent unclimbed (I think) wall (no. 18 on page 260/261) - thin and hard, but definitely possible.
I'm going down to Machynlleth with my family over the BH weekend, so I might nip out for a quick session if the weather and tides fall right.