How long does a Chihuahua puppy "generally" need to stay in training prior to competing in a show?

Well if you're giving a handler a totally green/novice dog, it will take some time to get the dog used to the show routine.

If possible, get your puppy out to handling classes, match shows, etc prior to sending the dog with a handler - it will save you time & money if you already have a solid foundation on the dog.

I've never sent one of my dogs off, I prefer to show myself, but I do know a handler that handles toys and non- sporting. She generally has a dog a month or longer before they're shown...she takes them to handling classes, grooms, show trains them. She takes them travelling to shows so they get used to the routine before it's ever time to enter a ring. It's not an inexpensive thing to do.