The Timeline should be edited in the Gantt window before going to Export Animation.

1. In the Gantt window, right click over the Timeline and choose Edit Timescale
2. A dialog will appear where you can add, remove, and edit rows of the Timeline. To change what is displayed in a row, use the drop-down menu on the right. In the image below, the default timeline is on the left (bottom row is in Weeks), and a modified Timeline with the rows changed to Year/Month/Day is on the right

 3. Before exporting the Animation, you may also want to change some of the settings in the Timeline tab of the Export Animation window. In order to show every consecutive date in the bottom row of the Timeline, you can change the Scale to Month. You may also edit the Timeline Start and Finish