Can someone help me with App Limits for a childs account

can someone please help me with understanding time restrictions on a childs account. I'd left it to my ex but it's been a disaster, what she thought was 'downtime' just turned out to be something that the child himself could 'ignore' which has led to damaging 12 hour stints.

I'm now in control, have set downtime to 'Block at downtime' so that's ok.. my actual question is understading app limits

I'm happy for him to have 2 ½ a day - i want that as a 'pool' which he can use as he sees fit. I've ticked all apps in the one grouping - Music is a big part of all our lives though so Spotify is a slightly different matter - i'd accept an extra 30 minutes use with that so if he wanted to listen to 3 hours of music but be able to do absolutely nothing else, then fine.

If I selected Spotify as a separate grouping and selected '3 hours' would than be a separate 'pool' ie, would he effectively have 5 ½ screentime?

[Edited by Moderator]