Is your father on medication? Your father should get some physical exercise...is there an exercise routine associated with the Senior Center visits?
It sounds like when your father has something to do, he enjoys being up and not sleeping. You may want to try getting him a couple of hobbies, just things to keep him busy, he may just be sleeping out of boredom. Everyone needs a reason to get up in the morning, I think it would help if your father had more things he could look forward to every day. Take care....
No, I don't think so it is the symptom of end of life. I lived with my father in law who was 94 years old when he came in. He's healthy, only with asthma. He offered help me to sweep the floor/yard. Hanging and picking up the clothes. He also concentrated on the weather make sure he picked up the clothes before it rained. He'll miss if he slept all the day long! LOL. He liked sleep (usually longer hour than us). He said to me, when getting old all the bones shrink, so can feel the body aching. He said exercise is important. Even he was on the bed, he also moving his toes and fingers a lot. He got up ate his meal about 4 or 5 times a day. Very little he ate. We also took him to go out with the family. Of course not walking, sat on the wheel chair. He die 6 years later. After the dinner. May be your dad has illnesses so he is a bit different. I wish him all the best. Take care.