Heidelberg Castle and between actions

Just to be sure if I understand correctly

Action player always have priority playing cards. But in the case of the Heidelberg Castle I can say in the "after resolution" window (before the action is completed) that I want to use my heidelberg Castle. In that case, I could (actually I must, I guess) use it after the current action completes and before the acting Methuselah plays any action. As the use of the castle is queued before the priority of the acting Methuselah.

Am I right?

Name: Heidelberg Castle, Germany
AKA: Heidelburg Castle, Germany
[DS:U2, FN:PR, KMW:PAl, LoB:PI, 25th:1]
Cardtype: Master
Cost: 2 pool
Unique location.
Lock to move blood, equipment and/or retainers between any two ready vampires you control. Cannot be used during an action.
Artist: L. A. Williams

www.vekn.net/forum/rules-questions/79166-correct-time-to-use-heidelberg-castle-germany-for-non-acting-player?start=12#102425

There is a window between every action where all players, following the sequencing rules have an option to use non-action effects. No one can rush-announce another action to prevent you from being able to use the Heidelberg effect (or any other effect).

Ok. I think that now I understand. Also, I can understand I can use HC even before the acting player even plays an action card.

Yes, there is such a window and after the last action too. Which doesn't matter much for HC since you can use it in any phase, but might matter for other effects, which are restricted to the minion phase.