You can add trash until the compartment is full and the compactor will not compact the trash any further. The compact cycle time will be shortened as the compartment fills up. During full cycle the ram travels 2/3 of the way down into the trash bucket.
With Humalog's short action time of 3  hours, covering postmeal highs with more insulin can be considered as soon as two hours if a meal dose have been underestimated. Of course, not as much sliding scale insulin would be needed here as before a meal, because some of the meal dose is yet to work.
Later in the day, I go by experience. If your blood sugar goes up when you exercise at 5, then take a little insulin so that the exercise will make the insulin go farther. In my experience, with a blood sugar of 171 at 5 pm, I'd take about 1 unit of Humalog to exercise.