What is the reset time for diminishing returns when feeding berries in PoGo gyms?

Question

When the latest gym rework originally came out, the diminishing returns for motivation increase on berries would reset after around half an hour. A berry fed half an hour after the first berry fed would give the same motivation increase, and diminishing returns would start again.

Lately I've noticed that all berries fed suffer diminishing returns after the first, and that berries provide less motivation than before. Do diminishing returns reset after a much longer period, or are diminishing returns permanent? I've looked this up here and on reddit, but I haven't found anything recent about berry feeding and diminishing motivation returns.

Answer 1

The timer for diminishing returns appears to be the same as the timer determining whether or not you can feed another berry at all.

From this Silph Road thread:

You can feed a pokemon 10* berries in a fixed 30min window that starts when the first berry is fed. This counter is reset after the 30min is up, and should you choose to continue feeding the same pokemon, a new 30min timer will begin when you feed it the first berry. For example, if you feed a pokemon 5 berries at 1pm and another 5 berries at 1.15pm, you will not be able to feed it anymore berries until 1.30pm, where you'll immediately be able to feed it the full 10 berries should you want to.

In the comments, the OP was asked about the diminishing returns, to which they replied:

After the 30mins, it's back to the state where you've never fed that defender before, so the next berry will be just like feeding the first berry in terms of motivation gains. About gold berries, they count towards the 10 berry limit, so if you already fed 8 normal berries, you can only feed 2 more goldens.