How do Digestion Buffs work?

The Player Handbook only states the following, as far as I’m aware:

Snacks may be consumed at any time by a Pokémon or Trainer as an Extended Action to grant a Digestion Buff. A Pokémon or Trainer may only have one Digestion Buff stored at a time unless they have the Gluttony Ability, and they made trade in this Buff during battle to use the effect of the Snack. Berries are considered snacks.

Emphasis mine. Now my question is: How long do Digestion Buffs last? Simply until they’re traded in? Or does this need to happen before an extended rest is taken? Also, how long does it take to trade in a Digestion Buff? It can’t be an extended action like it is to consume a snack, since it can be done during combat. Is it a free action, then? Or a standard action? Or something else still?