At Monarch we generally call 'Cabin Crew released' over the PA once we have retracted the flaps/slats and are happy we aren't about to hit some turbulence. (Or as the captain said the other day 'Cabin crew GET TO WORK'
). This would happen somewhere around 3000 feet + a bit above the ground.
We keep the seatbelts on until 18,000 (again if conditions permit to release the pax).