I had my gunite shot on June 18 and had the plaster applied the following April. That's an anomaly but the first month is very important that you keep it wet. You can nearly double the strength of concrete by doing so. I bought a garden soaker hose and ran it along the perimeter and kept it wet for the first month.
In my case, I didn't want to plaster and fill the pool in late August just to close it in September, so I went over the winter looking at the gunite eyesore. The time also permitted the ground to settle- in some cases over 18" inches, which would have been awful for my eventual patio.