Here's what happened for us. Simone had been separated from her brother at the shelter and I later found out they ALWAYS adopt siblings out together.
I don't know why they separated her from her brother at that time. Maybe it was better it worked out this way or we never would've gotten Snowball mth. later.
My Dad was in town for the weekend so the 3 of us (Dad, hubby and I) headed to the shelter. We brought Snowball home and HE was the one hissing. He had never lived with another cat before. He was just 7 mths. old. Right away he had to be everywhere I was. If Simone came near, he hissed. She'd walk up to him and sniff him without a care in the world and he'd hiss at her. You could tell she wanted to make friends with him. Finally at one point my Dad told Snowball, "Next time you hiss at her I'm booting you off the couch." He hissed, so, he gave him a gentle push on the tush and he landed on Simone. The look on their faces was priceless. They just stood there looking at each other like, "What just happened?", but no hissing. We just about died laughing. My Dad doing this makes it sound worse than it really was. It was truly funny. (No animals were harmed in the making of this action
) Snowball is very dramatic and always makes things seem worse than they are.
So, the first night he took over the bed. Simone was not allowed on it at all. He refused to let her on it. You could tell the way they were acting they weren't gonna fight. So, I put her on the bed with us. Snowball wasn't happy, but he let her sleep with us. I think he was learning that his hissing wasn't getting him very far. When I woke up in the morning the two of them were curled up together. That next day the 2 of them were playing and acting like they had lived together forever. So, in our case it just took that one night.