Richie–Rich your glass of water analogy is erroneous but I take your point to be once the base is saturated then it’s saturated. But the base material is never saturated until the wax has penetrated the entire 1.4 mm thickness which I believe would not happen. A better analogy would be to think of the ski base as an unpainted wall. The first coat of paint covers, but much of the paint is absorbed and thinly covered areas of the wall can be easily observed. The second and subsequent coats of paint are also absorbed but less so with each application and the appearance of the wall improves until more coats of paint will not make any observable difference in the color or texture of the surface. How many coats are enough?
Most experts (self proclaimed and otherwise) seem to agree that you can’t wax and brush a new or freshly ground pair of skis too many times. Each wax and brush cycle polishes the depth of the base structure smoother than the one before. One can conclude that there will be a diminished return on each successive wax, hotbox and brush cycle. In other words the improvement to the potential speed of the base will be most apparent after the first wax/hotbox/brush cycle and each subsequent cycle will add some speed (wax) but less so each time.
Dave Peszek wrote in SKI RACING magazine “Top technicians, like the USST's Jeff Butz, will wax giant slalom and slalom skis at least three times before the skis ever touch the snow, and speed skis at least 10 times.”
If 3 or 10 waxing cycles are enough for the USST then it’s a reasonable outside limit for anyone reading this forum. Since hot boxing is just deluxe hot waxing I invite you to draw your own conclusions.
I always let my skis return to room temperature overnight while still inside the hotbox. I believe that most composite structures react poorly to abrupt temperature changes.