My grandmother in law is 95 years old and she has dementia. She sleeps most of the time, only waking up because my mother in law makes her get up. She gets her up around noon-1:30, to have a light meal, sometimes just water. She will sit her down in her chair, where she will sleep for another couple of hours. Then wakes her up again around 6-7 for another light meal, if she’ll eat. Then down to sleep again for the night.
My 92 y/o mother lives in memory care and lots of the residents are asleep on the chairs that are all around the great room area, every single time I go in to visit. They're woken up to eat and toilet, and then they go right back to sleep on their favorite chair. The care givers do get them up in the mornings, get them dressed and groomed and bring them out to the living room area for the day, but again, they do spend the vast majority of their time sleeping.
It's tough to witness this, I know. All the best to you.