So this may be a strange thing to ask here, but how long does it normally take cats to adjust to each other?

We've had a cat for about 5 years now, ever since she was a kitten, and really the only other animal she's had for company is our rabbit, and he doesn't do much more than sit in a cage all day. We're moving in my soon to be stepfather and stepsisters, and they've decided to adopt a kitten who is now living with us before we move in. I know that its normal for there to be an adjustment period for the older cat, but its been three, almost four days now and it doesn't seem like anything is changing.

Our older cat, Bella, hisses and growls at the kitten every time she sees her. Now, originally Bella didn't even want to be in the same room as the kitten. Now she'll at least stay in the same room, but prefers to keep the kitten out of her line of sight, and when she does see her, its just constant growling and perhaps a hiss if the kitten gets too close.

There was one time where, while the kitten was sleeping, Bella got close and started sniffing her. But her sniffing woke the little one up and it spooked her, she hissed very loudly, and then ran off. It also probably isn't helping that the kitten sleeps in all her favorite spots. My lap, the blanket on the couch, and the back of my recliner.

If there is one change I've noticed, besides the fact that she'll stay in the room albeit out of sight, its that her growling seems to have gotten... lower. Like before you could hear it across the house, but now its more like a low rumble. I'm hoping that's a good sign.

If anyone here can tell me how much longer this is gonna last, I'd appreciate it. I should probably also mention that neither of them are fixed. I also know that normally you're supposed to separate them at first, but we don't have any rooms to put the kitten in. The house is cramped enough as it is and every room is in use at max capacity, so we've just given the kitten free roam of the house, though she tends to stay out of the upstairs, probably because that's where our other cat tends to spend most of the day.

Cats are territorial. It'll certainly take more than a couple days before the alpha is willing to compromise.

I have two cats, one is a kitten and one is an adult. I actually got the kitten in november 2015. It took a while before the two got along I think that around januari my older cat finally accepted the kitten but they still quarreled. I think for me the problem was the difference in age because the kitten wanted to play but my older cat just wanted to lay down. It all calmed down in March and now they are fine. My older cat only gets annoyed when the little one plays with her tail :3