Mine usually flowers in august. I have it planted in the ground behind my shed. I also have rogue plants here and there.
Cat nip will grow some really nice looking buds on it. Once it flowers the plant starts to die off and it gets kind of ugly looking (that's why it's behind the shed).
You can harvest it and dry it like you would weed to save for your cats in the winter time. I've never tried jar curing or anything though) Mine prefer it fresh than dried, but in the winter they have to take what they can get.
If you plant it in the ground it will grow back every year off the same plant. Not sure about pots, cold winters where I live kill off potted periennals so the ground is the best place to grow them for me. Sometimes if we get a couple of warm days it'll push out some new growth in the middle of winter. I always go pick it for the kitties to enjoy.
I've also heard of people smoking catnip but I've never tried it myself. Catnip is a good mosquito repellent. We rub the fresh stuff on us and put a sprig in our pocket when we're out after dark, helps keep us from being bit.