Until just recently, I marked time with the birth of my children. The calendar in my mind recalled the date of events in terms of who was born and who wasn't. For example, we owned a Chevy station wagon more than 10 years ago. How do I know? Because my 10 year old never rode in it. But alas, it appears those days are over.
Now I date my life in terms of which quarter I was in school. For example, it was during the Spring quarter that my neighbor moved out. Or, my son got his braces off during the Winter quarter.
Every civilization marks time in its own way. Right now, my own personal civilization happens to be marking time by the school calendar. Will it last? Yes, but only for events that happened during my school days. Does it matter? Not as long as the Holy One marks all our days with joy.