Saw your post about rather going over than under and thought I might add a late word of caution... These cacti can take you to another world completely with too much. 8 hours in a different world may be more than some could handle. Regardless of your past experience, I would say that it is easier to have more prepared than you might need and take more later on if you feel the need. The bottom line is you don't have to take your medicine all at once. It is perfectly acceptable to take some at 18:00 and more at 21:00 if your not feeling any effects.