Timothy hay can be fed unlimited (if your pocket stretches that deep!) It's one of the best ones for adult rabbits as it's high fibre, low protein, low calcium, and lovely and coarse so it's great for keeping their teeth worn down. I feed a good handful of timothy hay (2 different types and also a little of oat hay/orchard grass/brome hay too) to each pair every day, along with unlimited meadow hay. Much as I'd love to feed them unlimited Timmy hay, it's just too expensive and they are all good grazers and hay eaters so it's not too much of a problem. The only hay you shouldn't routinely feed lots of is alfalfa hay - it's fine for babies but is high protein and calcium so should only be fed to adults as a treat.