[2022] How will the city nodes work?

Metropolis (a maxed out stage 6 node) should generally be one of the most stable and established nodes. You won't see these get destroyed quickly, or built back up in a single day.

Node sieges enable players to destroy nodes. Sieges are started via a siege scroll, which is acquired through a quest that scales in difficulty with respect to the level of the node. A substantial investment is required to attain the siege scroll.

Once the siege scroll is brought to the node and is activated, the declaration period begins and a countdown is initiated for players in the region to see. This countdown runs for a number of days equal to the stage of the node being sieged. In the case of a Metropolis, this is six days. As a citizen of a specific Metropolis, you shouldn't be surprised by a node siege "the next day." To learn more about what we've shared about node sieges, see the wiki here.

As for the other part of your question, nodes won't ever progress to be maxed out in a single day either. How long it'll take to max out a Metropolis has MANY variables, and we spoke about this at length during the July 2022 Development Livestream Q&A, if you want to learn more.