Oh... and in answer to your question... it can take anywhere from a few hours to a few days to a few weeks - it just depends upon the cats.
Hubby and I live in a very small home and we have four cats - but started with one. We've also fostered one or two along the way. We don't have the ability to keep cats separate when we integrate them, unless they're small kittens where we can keep them in a crate for a while.
One of the cats we integrated was a bit aggressive, so we kept a large dog crate in order to separate him for a little while.
Basically, we used the vanilla trick, which helped some. But basically we just kept an eye on everyone, and whenever the fighting started to get too aggressive (meaning, it looked like someone was going to get hurt), then we'd break it up.
Spooky hissed and batted at Tuxedo (Tuxedo was the last one we integrated) for weeks - she just wanted her space, and he wanted to play with her. Lazlo and Shelly were secure enough in their alpha roles (I guess) to not have a problem with Tuxedo. But it took about two weeks before we comfortably left the home, secure knowing that we wouldn't come home to bitten ears or something. We always made sure one of us was home until that point.
We also used the bathroom as a "cool down" place. Whenever Tuxedo went after Lazlo, Shelly or Spooky in a really aggressive manner, or shaking a can of coins wouldn't deter him from the attack, we'd pick him up and put him in the bathroom with a few toys and some water.
However, that was only when we didn't have time to play with him. The first few days, in my experience, the hissing and batting is to figure out who's space is who's, to set boundaries and establish the pecking order. After that, it seemed to me that Tuxedo wanted to play and ended up annoying the others - pushed them too far. Sometimes it seemed more like he was challenging for the alpha position (which he has not successfully won yet).
Shaking the can of coins almost always stopped the aggressive behavior. Also, we frequently grab a fishing pole type toy and swing it his direction when he's bothering one of the other cats. The play will frequently divert his attention, and absorb his play desire and energy into the toy as opposed to being directed at the other cats.
But like I said, when he was undeterred, putting him in the bathroom for 15 minutes to half an hour worked. He'd usually be asleep when we open the door - and sometimes he was just playing by himself with the mouse or whatever we left in there with him, and when we opened the door he didn't even notice or bother to come out - until he flipped his little mouse out the door and had to get out to retrieve it.
Just tricks you can try in a small space.
Good luck, and keep us posted!