think about this

There must have been a way to decipher the language, to some extent at least, since so much is already known about their culture.

Since this is a discussion on time, people can use other methods, like those of the Aztecs who did indeed have pious dates carved into their calender, still made it effecient enough without a connection to religion/god. Sundials would work too, it'd get complicated trying to keep track of the years though....

Not to mention science which deals with seasons, just keep track of the equinoxes throughout the year. Or you could follow the waning and waxing of the moon....
 
The mayan calendar was the first calendar recorded in history. It ends in 2012. (The year 2012 has been estimated so it correlates with the calendar dates we currently use as a planet.) Jesus can suck some hairy ballsack because he didn't create any calendar. Comments?
 
I guess it would be kind of awesome if we all went into the fourth dimension and have our bodies transformed into pure energy like one of the theories, but I'd rather stay in human form and fuck some chicks :D