If you set it to Ask, as far as I’m concerned it is awaiting input (so it shouldn’t close); this isn’t in the same category as automated notifications were no action/input is required and the pop-up would close after the set duration.

That is obviously my thoughts and apparent alert pop-up action, not necessarily correct.

I don’t know if there is a limit, but most people are going in the other direction, for me I have alert pop-up duration at 10 seconds. I have all my shield actions set To ask as the first action and I have never seen the alert pop-up disappear until I choose the action to take.