(Just from observation during chap 21)
It works on all buildings that produce mana as their PRIMARY production.
So it works on the Maze when you collect the 3-hour production, but not the DA as far as I know as the mana is a result of the spell being cast.
It does work on the Ashen Phoenix, as it produces mana as primary and then sentient goods and KPs as secondary bonus, but does NOT work on the Polar Bear for instance as it's prime production is Coins, and then mana, seeds and a PP spell as bonus production. So most of the evolving event-buildings will not benefit as they generally produce mana as a secondary bonus.
I am not sure about things like the Genius, but I doubt it works on those. Can't see it on the production.
Best use for it is to put out all the eventbuildings that produce mana you have and/or regular manaproducing buildings. So Burning Pool, Lava Egg, Mana Hut, Galactic Phoenix Egg etc as event buildings and Dragon Rock Gorge as one of the regular cultural buildings from the tech tree (or of course the premium ones that need diamonds).
You can see the mention of the expiring building on the one and the lack of that mention on the other of these event buildings. The mention will be there on all other buildings that are affected too.
(And yes, I know. I accidentally hit the Ashen Phoenix twice with petfood while it still had some left from the last event. Oh well.)