Dear Bluebelle3,
I've sent you a reply to your earlier question in the Pre-Diabetic section on this site that should explain a few things.
As to this specific question, the time will vary depending on the individual, and their pancreas recover time from having to suport the growing infant before birth, and what may be their insulin resistance. It's usually a few weeks, but with multiple GD it can sometimes take quite some time longer for the body to 'normalise' (maybe in extreen cases 3-5 months after giving birth).
You should also be aware that having had GD also gives an increased long term health risk to both the mother as well as her younger children to either/all of them eventually going on to develope diabetes in it's conventional form (usually type 2) at some time later in all their lives (often many years) and in many instances a Dr as a precaution will instigate regular B/G tests ,say once a year just to see if there is any changing pattern that is developing within the individual.
Hope this answers your question - Best regards - Lazybones