We have a 10 month old male cat (virtually full grown) and we recently adopted a 6 week old male kitten. we did everything the internet recommended regarding this situation (separating them in different rooms, letting them smell each other's scent and then supervised mingling).
At this point we've had the kitten for a week and a half, during which the cats have been mingling quite a lot but only under our supervision. During those mingling sessions sometimes they play nicely but a lot of times the older cat gets anxious and too aggressive - he bites the kitten really hard and twists him like a ragdoll, making him scream, and then we step in and break up the fight usually by removing the kitten from the situation.
We are concerned that if we are not there to supervise, the older cat might seriously harm the kitten and are anxious about the possibility of leaving them alone.
My question is, how long should we continue with this routine of separation when we are not home and at what point would it be safe to leave them alone?