The original idea behind natural HP healing in 3e was that since HP represented much more than just physical damage, that more experienced characters would recover them faster than less experienced ones. That said, the natural healing rate was set at 1 hp/level per day. Thus, a 6th-level character would get back 6 hp/day.
That said, it appears that the (1 + [positive] Constitution modifier per character level) equation means that either the character gets (1+Con bonus)*level Stamina/hour or 1+(Con bonus*level) Stamina/hour. Of course, that's per hour of rest, which would preclude things like driving/piloting a vehicle, performing maintenance, etc.
That would mean a 7th-level character with a 16 Con would recover 28 (or 22) stamina in an hour of rest. That would mean that the character recovers all of his stamina derived from his constitution bonus in an hour, plus 1 (or 1*level). An average character with d4, d6 or d8 hit dice completely recovers from 0 stamina within 2 hours, and an average character with d10 or d12 hit dice completely recovers within 3 hours. Using the example on p.216, however, means that the same 7th-level character with a 16 Con would completely recover from 0 stamina in 10 hours (d4), 12 hours (d6), 14 hours (d8), 15 hours (d10), or 17 hours (d12). That's 10-17 hours of nothing more strenuous than eating, reading or watching the news. I just think that's too long for "heroic" characters to be down in the middle of a story.
However, the equation example conflicts heavily with the second equation on p.216, in that a character heals 1 stamina in a number of hours equal to 1+|(negative) Con modifier|. Whereas (accoring to the first formula) characters with a 16 Con are recovering from 0 in 2-3 hours, characters with a 6 Con would take 5-9 days. IMO, that is too much of a difference in recovery times, so the example (just 1+Con modifier) would be more accurate (although I still think 10-17 hours of rest is too much recovery time for a heroic character).
(Note: For the "average" 7th-level character with 16 Con, I used the average number of hp per level based on hit dice, so d4 HD would have 39 hp, d6 would have 46, d8 would have 53, d10 would have 60, and d12 would have 66.)