as i mentioned else where time is not an invention of man, that is like saying gravity is an invention of man (whether you believe on RE gravity or FE gravity - lets just call it gravity for now so i don't have to think of another word for it)
time is defined as how long it takes for light to travel a certain distance, for example one second is how long it takes light to travel about 300,000 km.
Yes seconds, minutes, hours, and months are all "human" inventions, and broadly days and years too, although they are more inventions of god/random chance (which ever you beleive made the earth rotate on its axis and around the sun at a certain speed). However society would work just as well if you defined minutes as 100 seconds, hours as 100 minutes, days as 20 hours, months as 20 days, and years as 10 months to make it all nice and decimal.... although you would have to redifine the lenght of a second, or not follow the rising and setting of the sun to define what time of day it was, and also not follow the rotation of the earth round the sun to define when a year starts and ends. but you could do it.
but anyway i ramble on. to say that time is an invention of man is lunacy, if humanity didn't exist it would be there just as much as it does now. how man records time is mans invention.... so saying tuesday the 29th of January 1980 is an invention of man would be correct.... if perhaps a little pointless to say.