You can use the Today marker shape to display the current date on your timeline each time you open the diagram. You can use the Elapsed time shape to show the time elapsed from the beginning of the timeline to the current date.
Add a current date marker
From Timeline Shapes, drag the Today marker shape onto your timeline. To change the placeholder text, click the text, and then type.
Add an elapsed time marker
From Timeline Shapes, drag the Elapsed time shape onto your timeline.