This question is not relevant when using a robotic lawn mower, as the operational concept is different than with a standard walk-behind mower. While using a standard walk-behind mower, you have to wait until the grass grows and then mow the lawn. Once you decide to mow the lawn, you will generally complete the job on the same day in a few hours (depending on the size of your lawn), as you are not limited by energy factors (fuel, or electricity).
With a robotic lawnmower, in most lawns a few operations are required to cover all of the area. The idea is to maintain the lawn so that the grass is cut a little and often, and the lawn always looks well-maintained. For these reasons it’s not relevant what area is covered in one hour, as your lawn always looks as it was just cut.