How long to lock up kitten?

We got an kitten last week who is now 9 weeks old. We have been locking her up overnight to keep her safe. How long do we need to keep doing this? She hates it and will cry for up to an hour after we lock her in. We also have a 12 year old dog and 11 year old cat who are not locked up. Dog pretty much ignores the kitten. Cat hisses when she sees the kitten, but no other aggression has been seen.We have a 2 story house and she isn't good on stairs yet. We were afraid she would tumble down the stairs again.

To be safe from what? From your other cat you mean? I would imagine you would have never had to lock the kitten up in the first place but that's just me.

You do not have to, as long as there are not any small objects she dan eat. If so, clean them up and then you can let her out.

You don't have to lock the cat up

At nine weeks of age, the kitten should be kept in the bathroom even during the day, unless you are playing with it. Kittens can get into too much trouble or even get seriously hurt, stepped on, etc. This also gives the other cats a chance to get used to the kitten. Do this until the kitten is around 12 weeks of age, or so. Be sure it has its necessities in there, too.She may become a little quieter, at night in this case, too. Otherwise, you might consider bringing the kitten into the bedroom with you, but be sure there is a litter box very close since kittens often forget where the box is, at night. This is an additional reason to have the kitten closed in the small room with its box: they often forget or play too hard, and miss the box at this young age.