Very complex question.
Generally, on "average" for the GJ's about 3 months (2 @ 30 days and 1 @ 31 days), 4 days, 22 hours and 7.5 minutes.
The Dragon Wings? Until after all of us and our children are dead.
Seriously, there are so many variables such as quantity produced, popularity of specific model, local availability, etc. that affect prices. Market conditions will vary from region to region. If you can't find a fair price in your area odds are you can somewhere via the net or mail order - within a "reasonable" amount of time after release.
What is a "reasonable" amount of time? Again, that depends.... It is very rare that a model is so much in demand it's retail price goes up sooner than you can blink or take a dump - but it does happen on occasion (Herpa Peter Max, GJ Formula 1).