Why does the graph draw very slowly?

Select Computer Disk Ephemeris in the main menu and calculate disk-based ephemerides for the years you need.
Also select the Read ephemeris option instead of Compute ephemeris option.
If a particular transit-position ephemeris file (*.GLG file) does not exist, Timegraphs will automatically go into Compute mode and the graph will draw slowly. If the *.GLG files for the selected years do exist, and you select Read mode, the graph will draw much more quickly.