Yes, as allready said, it is possible. Same as it is possible that the person in front of you at the supermarket line stole the cash and the cashier gives it to you as change. But even IF you get stolen coins, as long as you got the legitimately, you dont have to fear anything.

Now how long do you have to wait. While bitcoin core suggests you to wait for 6 confirmations in the network, Im usually fine with only 2 when I get payment <1 bitcoin. If you feel insecure about this, wait for 6 confirmations.