They obviously do take it seriously or they would not have asked. I’ve seen kids who were always on time but put in a half ass effort when there. It isn’t the kids fault, so if they are ten minutes late and the kid is a good player who works hard that should be enough.
In our league, over 200 boys tried out for 60 spots in my son's year. There are sufficient good players that you can find enough kids who will be good players and also show up on time.
I'm the team manager for my son's team, and it amazes me that there are parents out there who pay $2300 for travel soccer, and then don't have their kids show up on time (or at all) for practices, games, and tournaments. And that makes a big pain in the neck for the coach, and for games and tournaments, for me to try to scrounge up guest players from other teams or rec who want to "guest play" for us. It is horribly inconsiderate.