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.
We usually don't have any trouble if we dose after 2 hours, but we have an exceptionally short duration of active insulin. In general, I think you're fine as long as your ratios are on and you don't correct more often than every 3-4 hours. Question - they told us not to dose the humalog more often than 3 hours apart.