Does anyone know when female dogs have their first season?

Typically first heat is between 6-12 months.  "Mini's" are bred down and have the potential for TONS of health problems.  I think it's harder to tell with a dog that small.  However, my best advise would be to get her spayed ASAP, before she ever has her first heat.

glenmar

However, my best advise would be to get her spayed ASAP, before she ever has her first heat.

I definitely agree. I personally find dealing with a dog in heat unnecessary, and do not enjoy it. I would spay her before she ever goes into heat.

Thyroid problems can cause irregular and delayed heat cycles.  You might want to get that checked. 

Some of the tiny dogs will have a season and you won't notice!  With some, there is little bleeding and the only sign might be slightly enlarged vulva.  Obviously, if you are asking the question, you are a pet parent and not a breeder, so my advice is to go ahead and spay her. 

Even if she had thought about breeding, the "mini" is not recognized by the AKC and for good reason.  You can only size down or up a breed just so much before you run into serious risks of health problems.

 Toy sized dogs often wait til 10-12 months. I prefer my bitches go through one season, for their development, but I guess I'm weird. Nobody LIKES a bitch in season, but.... it's part of life.