I am an ESO Plus subscriber, so normally when I log in I see the "Champion Points Gaines at an Accelerated Rate" message. I'm so used to seeing it that I don't notice it.
Yesterday I had an unusually long run of hitting strongboxes, each of which net me 4k xp (I am champ level 203). Eventually - after a couple hundred (?) of them - each strongbox started netting me only 1k xp. I also noticed that the quest reward xp was much lower than I was used to seeing for large quests.
I logged in this afternoon and popped a strongbox. 1k xp.
While I was crafting, I suddenly saw the "Champion Points Gaines at an Accelerated Rate" message appear. I immediately hit another strongbox. Sure enough: 4k xp.
So is there a cap on how much accelerated xp you can gain in a particular day? When does it reset?