Once you receive the product is the screen wrinkly or flat when stretched and mounted. How long does it take to get wrinkles completely gone?

It unfolds with creases, but if the weather is warm it will all work itself out once you set it up over a couple hours. Some stubborn creases can be worked out with a hairdryer on warm setting (high will work well but be careful not to leave it in one spot too long). If you can set it up during the day it should be ready to go by night (might have one or two light creases).
Keep in mind the fact that once you put on the projector, due to the bright light you won’t be able to see small creases so don’t worry about them too much.

For more information please check out our guide setting up a great backyard setup
http://outdoormoviehq.com/ultimate-guide-to-outdoor-movies
Or take a look at our recommended projectors and screens
http://outdoormoviehq.com/outdoor-movie-screens