World-of-warcraft – How does the Heart Of Azeroth azerite reduction work

If we were to compare it to WotLK and you're inquiring about obvious effects of the surge, like queues, etc, I'd say a week to a month depending on the size of your realm. The more players on the realm, the longer the surge will last. However if you're referring to the crowding in the starter zones, e.g. Vashj'r or Mount Hyjal, that's already starting to dissipate as people spread out over them.

The "five second rule" no longer exists in Cataclysm. You have a fixed rate of mana regeneration while in combat, and another fixed rate of mana regeneration while out of combat.

Out of combat

Your out-of-combat mana regeneration rate is based on your spirit. "Mana per 5 seconds" (MP5) no longer exists on items, and has been replaced by spirit. (You'll still see it on mana oil, though.) Every class that has a mana bar will regenerate mana this way while out of combat.

In combat

All classes start with a baseline regen rate of 5% of your base mana per second. (Base mana is the amount of mana you would have with 0 intellect.) Classes using healing talent specs gain a passive ability called Meditation, which lets half of your out-of-combat regeneration continue while in combat.

For non-healing specs such as mages, warlocks, and shadow priests, spirit does absolutely nothing for your combat regen. Many talents and abilities exist that give you bonus mana in combat, however: Replenishment, Archangel, Hymn of Hope, Shadowfiend, etc. Mages can passively regenerate mana using Mage Armor.