Yes it will take a couple of weeks and sometimes more. You just have to be patient with them getting to know each other. Since they are both kittens, they will soon be best friends! Older cats are a little harder than kittens, and takes a bit more time. They will probably have an occasional spat and that's normal, but since they are kittens they wont hurt each other, they are just setting some ground rules right now. They can be quite volcal at this time, but that's all it is, so dont worry, I'm sure things will work out for them! Good Luck!