In the stockmarketgame, when I sell a stock, does it sell at the price when it was sold or the value of it 20 minutes from now?

the most basic thing you have to understand about the stock market is -

For every sale there has to be a buyer -

With common stocks this dont matter cos they are traded all the time , so when the order goes in to "sell" they will be sold withing a few seconds/minutes, AND the difference between selling and buying price wil be small. but with uncommon stocks it may take some time for the broker to find somebody to buy so it could take much longer to find a buyer . In this case the "market maker" will buy them, and sell when they get a buyer. BUT the price you sell at is likely to be different from the one you see on screen

In any case- does it really matter? -

prices are going up/down all the time - the price between "now" and 20 minutes from "now" is just as likely to go up as down

IF YOU SET TO SELL AT MARKET PRICE, STOCKS SOLD INSTANTLY IN SECONDS BY PICKING THE PRICE AT THAT MOMENT AND HAS A BIT LOWER OR HIGHER.

IF YOU SET TO SELL AT THE PRICE YOU WANTED, STOCKS ARE SOLDED AT THE SAME PRICE OR A BIT HIGHER,TIME FRAME CANNOT BE DETERMINED.

it sells for the price at the time you issued the 'sell'

It will be sold for the price in effect at the time that it is sold.

If it takes your broker 20 minutes to sell and the price drops in that 20 minutes then . . . life sucks.

Nobody ever said life was going to be easy, fun or fair.