I had the same issue. If they are in middle of something that is streamed, such as youtube or some roblox games, it will continue until the stream is over. I was annoyed, to say the least. Sometimes it also doesn't do the breaks, when this happens I remove all of the breaks and put them back in. I found that time limits are useless and started using Google Family link instead (only works on chromebooks and android devices though).
Pausing devices doesn't work at all for some of ours, including iPads. Devices just continue as normal even though they show up as paused in the xfi app.