I keep mine in for about 3 weeks when they're in a new house. First time of letting out is done before food time and under supervision. Once they're confident, you'll be fine to let her in and out as she wants. You'll panic once she goes out of the garden, and wait nervously till she comes back. :D
Yes, definitely three weeks. It will soon go and it's not worth the risk of letting them out too soon. They have to be really familiar with where they are living and regard it as home before they go out.