I'm not sure exactly how to have this feature.

But I'm just going to describe right now what I want to do and how I might possibly do it:

A certain number of interactions in the form of "turns" (talking, moving around, etc) will eventually trigger a message which will announce that its now night. This results in the player entering a "monstrous" state (implemented through player attribute menu), in the new form the player will be limited in certain ways (not being able to talk to npcs only attack, not having access to inventory, etc). But after a specific number of turns the player will revert back to normal "state" as it is now "day" (as announced in a message).

Or do I maybe create another "player" object and have the player switch over to the next "character" briefly, than switch back, again after a certain number of turns .

I want to make a game similar to Zork, in gameplay not story (maybe I might throw in a few references though as an in-joke).

Feel free to critique the two methods I mentioned and let me know what I could do better:)

Quest allows you to switch the POV ("point of view"). You could, as you say, have two different player objects and then switch between them. (I have never done this myself, so I don't know all the details, but you will need to move the objects around when you switch, as you'll want the monstrous character to be in the same room the other one was, the other one to not be there, etc. That might play havoc with the room enter scripts, so keep that in mind.)

As far as the behaviors you described, not having access to inventory can be as simple as removing the objects (if you switch POV, that will happen for you automatically). But other things are more command-dependent, so you're going to need to put conditional code in the ones you care about (e.g. talking to other characters, taking and dropping things?) to make them behave as you wish.

I think the big part of this is going beyond non-specific, high-level words like "not having access to inventory" to actual details like:
1) After the switch, the player will not have anything in inventory (or do you mean they have inventory but can't use it?)
2) Can't take objects
3) When they switch back, their old inventory will reappear

If you can get it down to that level, then implementing it will be much easier, as you'll have a task list to work through (and others will be able to help you more easily if you need help).

(Also, I'm not sure what you meant by "implemented through player attribute menu".)