Cadair Idris?
It’s a good 3 hour ride. Depending on your fitness it’s about 2 hours pushing and riding to the top and then a half hour or so down. Plus a half hour for sandwiches at the top.
Good variety of terrain, some technical sections and some flat out blasts.
Get some funny looks when you take the bike to the summit, but it’s got to be done, right?
Other than that, I think there’s some stuff out barmouth way. I spent easter in Dolgellau and had a couple of rides mapped out (that i had found on the internet).
If they’re likely to be of any interest I’ll see if I can dig out the links.