People are judging the Donut Mechanic too harshly.

There's nothing wrong with having a timer and yeah, at the start of the DLC, it'll feel like you're missing out all of the Pokémon that you can catch, but here's the thing, there have been multiple instances where that same portal with the same Pokémon located at that portal is back for you to jump in and finished what you left off.

Remember, the portal recommends you to feed Hoopa a donut with the same star level as it or higher, that way, time doesn't drop fast. I have seen many people say that it's difficult to earn berries in this games and it makes me question what have they been doing with them. I had 0 berries when I played this DLC without any knowledge that I need them. Hyperspace SHOWERS you with Hyperspace Berries as well as Exp. Candies the more you keep popping floating Poké Balls and especially the golden Poké Ball carries a bunch of items, so there should be no way people are wasting berries that fast.

And then there's the Rouge Mega Pokémon boss battles that some criticize for also having a time limit. Did you know that once time is up or you get blacked out, the game allows you to jump back into the match where you left off? There's no need to completely start the whole battle over with the Pokémon at full HP unless you want a challenge. Of course, this begs the question, "why does the timer need to be in these battles in the first place" and your guess is as good as mine.

That's pretty much all I can say about how you use your donuts. Because you get a bunch of Hyperspace Berries the more you're exploring around the Hyperspace Areas to find those floating Poké Balls. That's pretty much what I do after fulfilling a list of things to do.