Ah, well you'd have to ask them. In 1999, when i began the Buddhist practices of meditation, I started with 5 minutes per day and it was enough to keep me anchored and get results, and expand the time and depth of practice. I still only average 45 minutes per day but i augment that with "spacing out" practice where i just stop everything and return to meditation.
Or it could mean that in only 5 minutes time a meditator can reach the deep end of the pool. But for me the longer i sit, the deeper the pool is.
Five minutes is great goal for the "spacing out pratice" - to stop and remember the practice. Maybe thats what they meant.