You wouldn't send your kid to a sleepover without telling the parents about your kid's allergies or bedtime bugaboos. Why not use the same logic with screen time rules?
We know it's hard to do. It can feel like you're being judgmental or don't trust the other person to take good care of your child. But if you have strong preferences about what and when your child consumes media, you need to speak up even when you're not around to supervise.