1. Even though transactions don't confirm for a while, they send instantly. You would just have to wait a while to confirm that the person couldn't double-spend.
2. Exchange accounts are not wallets. When trading on an exchange, you are
not sending a transaction to the other party - the exchange is just transferring the numbers in their database from your account to theirs and vice versa, the numbers representing the coins which they are holding.
So basically, trades are executed instantly. The only downside is that you have to trust the exchange with your coins, which
in crypto is a big minus.