I found a fix!! Well at least a hack that I stumbled on that is working.
I was having the same issue as others, when applying a time limit of 1 hour of TikTok on my kids phone and seeing them log 2-6 hours a day.
FIX: On my iPhone, under the settings for screen time app limit under your child’s name, I simply changed the App Limit for TikTok by clicking “Edit List”, the click “Add” and adding a second app to the limit. Mine now shows “TikTok & Instagram = 1.5 hrs”.
For the last week I’ve noticed that it’s been working with my kid logging exactly some split of 1.5 hrs between the 2 apps.
I tested it by one day removing the Instagram app from the grouped time limit and sure enough my kid logged 4+ hours on TikTok that day.
Hope this works for you!