They should take all the time they need. Act I and Act 2 were great in DOS2, however Act 3 and Act 4, the quality dropped significantly. I fully expect the later acts to be a little less fleshed out than what we currently have, after all there aren't as many testers because we only get to play Act 1.
However keep in mind that the existing game already faces a lot of criticism since day 1:
The evil storyline is bad. Siding with the Goblins is poorly written, lacks any incentive, makes no sense and has terrible rewards and likely less content because you kill Tieflings that would otherwise make it to Baldurs gate.
They need to add more npcs favouring the evil storyline, why would anyone decide against helping the grove, after all thats where 99% of players end up going first? And unlike the goblins they won't need dice checks to not get attacked.
The balance is simply terrible:
Candle dip is free and unlimited dip in fire, makes poison bottles obsolete.
Food, Scrolls, healing potionts are too abundant. Food acts as better healing than healing potions during combat.
The game has way too many scrolls, Mages surpass all other casters because they can learn any spell. The headband of intellect is overpowered and causes players to cheat up to 10 stat points of intellect.
The magic items like Circlet of Scorchin ray uses intelligence instead of the Warlock casting stat Charisma, which means its terrible for Warlocks, which would really want an item for more spell casts. All magic items which grant spells should be equally viable by using your characters casting stat.
Shove, Jump is OP. Attacks of opportunity can always be negated and free backstab is always possible due to using jump behind enemy.
The entire resting system needs a big rework.
Short rests are obsolete because Long rests are still unlimited, which makes no sense. Long rests must be limited in some way. On the other hand, a ton of story is tied to long rests, some of these should maybe play out in short rests. At this point players are long resting not because they need to, but because they want to experiecne the story and they would miss out on it otherwise.