Birthday, new year etc all are useless stuff

What is the basis of measurement of time? Of course it is the division of time period of revolution of earth to the sun. All our measurement are based on this event. Our day is just time taken by
earth to rotate in own axis. Hour minute and second are only division of the one day into parts. Month is time taken by moon to revolve around earth and year for similar for earth and sun. Then if earth takes 100 days to rotate around sun? Or if our days shorten to 12 hours only? Or if we transferred to another planet who has own measurement of time? Then when will new year? When is your birthday! It is obvious that the time measurement should be re-defined. Our calender and clocks are only made to our simplicity so that we can work easily. And as we know there is no absolute time then what is the benifit of celebrate new year or birthday? They are just useless stuff who believes in relativity.