A few quick questions about the Fortress upgrade

I had a couple of questions for the more experienced players, and I figured an open discussion on the forum was my best bet at an accurate answer.

1 - When upgrading a Fortress to level 2 from 1, does the "hidden" mechanic of the upgrade start at the 12 hour mark, or does it need to be fully upgraded before it "hides" friendly units from view. I ask this because, upon reaching the 12 hour construction mark (3 out of 4 hitpoints), the Fortress is visually upgraded on the map - which would lead to me assuming that it does in fact enable the "hidden" feature.

2 - Does a Fortress upgrade in a providence that doesn't hold any allied units, but does hold other upgrades (say, a Harbor and a Railway), still provide a damage-reduction defense bonus against bombardment, or does a Fortress strictly reduce allied unit damage received? For example, will a fully upgraded providence be razed quicker without a level 5 Fortress than with a Fortress, relatively speaking - if no troops are stationed within that providence? In other words: is a Fortress bonus all-inclusive?

If these specific questions were answered elsewhere, I apologize for the waste of time - I generally know most of the nuances of the game and realized there is just a few, more specific questions I haven't seen answered anywhere. Thanks!