Resident Cat is Annoying New Cat

I have a kitten, Molly, who is almost fully grown, she will be a year old on May 9th. I adopted a cat from the SPCA, Banchee, on the 22nd of April, and he is almost 5. He is very thin. Molly follows him around but doesn't growl or anything anymore. Molly will stalk him and jump on him and pins him to the ground on his back and they get in a fight. He growls when she comes near him and when she does this and I think it really annoys him. I don't think she is hurting him but I am not sure what to do. She is a very active cat so maybe she is trying to play. I don't know if the problem will get worse and they will hurt each other, or if I should separate them. I do put Banchee in the bathroom at night when I can't keep an eye on them together, and I've been putting Molly in her carrier whenever she jumps on Banchee.

That is pretty standard. Resident cats usually won't accept any cats in his/hers territory. I would cage the new cat if the situation get out of hand. Let only the new cat roam under your supervision only.

So when will they find the truce? some 1 week, 1 month but my Don and Maya took 2 years to accept each others and still shaky

Thanks, that makes me feel better. They still fight but I hope they'll be friends someday

They can be depending on how long you separate them. One of them will have to get it. Put the resident in the bathroom sometimes too. Switch it a few times but make sure resident still knows that you know she was first.

Also be sure all nails are kept short so they don't hurt each other when getting into the squabbles It takes time and patience - weeks and sometimes months before they are ok with each other. I'm assuming that both are spayed and neutered.