Just make sure not to leave in the middle of a game.
Once you start up a game in Overwatch, you’ll usually be paired with the same group of people once you’ve matched up with them. This means that you’ll get to play a variety of matches and different maps with the same people, but with the occasional team swaps. However, if you want to take some time to go open your new Loot Boxes, or join up with a friend, or even just switch it up and hop into a new group instead, you’ll have to leave the group.
Make sure not to leave in the middle of the game, as this will result in you getting a leaver’s penalty where you’ll lose 75% of your gained experience points in the next game you join. It’s safe to leave when the stats screen shows up after the Play of the Game has been revealed. To leave, simply bring up your options menu and select the last option that allows you to leave the game. Do note that if you’re in a party of friends, this will cause you to leave the party. However, if you’re the party leader, you can leave the game and take your entire party out of the queue with you, and then join a new match.
When the leader leaves the game and starts searching for a new one, the rest of the group members will be able to go open up their Overwatch Loot Boxes while waiting too.