When do you know its the right time or best to move spouse to nursing care facility?

The time is right when your wife is no longer safe in her environment. From the brief intro you gave, describing her inability to get to the front door or know where the kitchen is, I would suggest her safety is in question. Doctors don't generally leap to conclusions such as this one. It's a difficult time, and a tough decision to make.

Do you have caregivers coming into the home to give you time for yourself, to exercise, shop, see friends? That might extend the time you can keep her home if she's not wandering.