No set schedule. A cockatiel's beak doesn't need to be trimmed unless it curls way under and prevents it from eating. However, this rarely happens. The beak is usually worn down by a cockatiel chewing on natural branches or using a cuttlebone. If your cockatiel should ever need a beak trim, only go to an avian vet to get it trimmed. Your avian vet is the only person qualified to trim a pet bird's beak.