Undescended testicle question. How long do you wait for the baby's testicle to come down?

6 months. If baby was full term. Hopefully before age one year. Up to one-year if born premature. Some testicles appear to reascend, these should be brought down as soon as they appear incompletely descended. General urologists may feel uncomfortable operating on babies in which case see a pediatric urologist or pediatric surgeon.
Depends. If the testis is not palpable either in the sac or canal by 6 mo some would explore the abdomen or canal at that time. A palpable testis located high in the canal might be given a bit of time, but by a year most would want it down.