In the old days (1960-2010), I could tell you roughly how many minutes had passed as I did things during the day. I had really effective internal alarms I could set that would get me to meetings on time. I really never needed to set an alarm clock for the morning although my obsessive-compulsive tendencies usually pushed me into setting three.
I loved the passage of seasons and months and years. I knew what had happened during different years.
Now … keeping track of the days has gotten difficult. Keeping track of time within a day has become a disaster. Most recently I feel like I am losing my sense of months and seasons; most recently I have started to ask myself whether it is early spring or fall when I go outside in the morning, April or September. I am amazed when a year or month or day has passed and have no internal sense of the passage of time.
I seem to have lost the sense of time in stages. The mind map below shows how it worked for me. I do not know if this is generally true for the typical person with dementia-neurodegenerative disease or if it something idiosyncratic to me.
This is clearly an area that needs further study.
Click on the image to expand it.