I've hunted there opening day many times... It is often busy as archery season for deer is open too. If license sales are any indication this year may be very busy.
If DEC follows their usual practices Stewart will be stocked the weekend before October 1 for the youth hunt. By the 1st the birds will have dispersed from the immediate stocking places. That's Okay... we need guys out there to beat down some paths from the parking areas into the fields!
All that said, I've always found a place to hunt there opening day.