The short answer is that you will never need to. Blotter is intelligent enough to automatically expand the viewpoint based on the data in your calendar.
Without any events, the view would look something similar to this:
As you can see, the viewpoint range from about 9AM to 5PM.
Now let's add a late meeting and see what happens.
As you can see, the view changed. Since our latest meeting spans until 10PM, so does the view point.
If we now add a meeting at 7AM, the view will expand from 7AM until 10PM.
Because of this intelligence that Blotter has built-in, there is no need to manually set the start and end-time for the day.