Hi all, when can objects held by characters be used exactly?

For example, the Casket, Rod of Ruin or Potion of Strength. They don’t specify when they can be used.

So could I use the Rod of Ruin just before an opponent tries to unlock the Portal of Power? Or the Potion of Strenght after an character encounters me for a battle?

Thank you!

There's generally no limit except what's written on the card and you can't affect combat after the rolls.