At what time was the calendar created?
In what period did the timetable initially devised?
In which period was the timetable come into existence?
When did the timetable originally created?
During what period did the schedule originally thought up?
At what time was the schedule firstly devised?
At what time was the timetable inception?
In what period was the agenda come about for the first time?
The Maya Calendar System Smithsonian Institution