Screen time on kids’ devices

I’m having issues with setting screen time limits on my kids’ iPads. Firstly, I don’t get notifications asking me for more screen time. Instead, it pops up on my kids’ iPads and they simply choose “one more minute” over and over. Basically, they are bypassing the screen time limits and can click “ignore limit” as well. I also want to allow iPad use between 4:30 and 6:30 pm each day, so I set it that way and my son was still able to get on at 3:30. Do you set the time for when you want to allow use, or set it for when it should be restricted? Screen time either doesn’t work consistently, or doesn’t work at all :-(. I just want to “set it and forget it”.