It specifically calls out recharging it to 50% every six months, so I assume it's a month+ kind of long term.

Also Apple seems to indicate that storage in a deep discharge state is far more damaging than storage at near-capacity based on the wording.

So if you're in doubt, charge it before you store it.

Finally, I don't think there's anything on that page that says you shouldn't keep your laptop plugged in when it's at 100%. I would be very surprised if they didn't have some cycle-conditioning going on. I have both a 2008 unibody and 2010 MBP, both essentially remaining plugged in for years. I don't think the battery life is abnormally low for their age, they still are capable of several hours of usage on battery.