When the size of the graph is set to automatic, in the Canvas settings, the axes labels will change when you have more room. For Dates, there is an option in the Axes settings to show two lines. When you do, you will see the Date shown below, along with the time above.
If this graphic is for a publication, you might want to set the size (or something close to the final size) so you can see how the automatic settings look.
How to set the graph size