It varies. It could be early as three weeks from the beginning of the medication to make the medication effectively. Remember, it simply slows down the progression, not cure. I would stop the medication when the person is becoming more chair bounded or bed bounded or no longer accepting to feed. Remember Aricept (donepezil) deal with three main components - behavioral, functional and cognitive.
Depends. The key to make this drugs successfully is to have socialization and to keep busy for activities. Also make sure the other medications does not cause worsening of confusion. Have a geriatrican or geriatric pharmacist to review them.