You'll always run the risk of a person accepting a better offer elsewhere. Same in every field, right? If she's good, you've have competition, no matter when you hire her.
Start looking for the best person you can afford. Treat her well, and you'll be on your way to success. Good luck.

I would start interviewing 8-10 weeks prior to returning to work. This will allow you enough time to interview and hire a nanny. If you start earlier, you run the risk of the nanny finding a new job.

My husband and I are expecting our first child in early April, and I am planning to be on maternity leave through the first week in August. I would like to find a nanny who would start the second week in August, and would work Tuesdays-Thursdays from 7am-6pm.

When (how soon) should I post this nanny position? When should I start interviewing?

Thanks!