Weekly lotteries 24 weeks out for 60% of trailhead quotas, then the Friday leftovers and a seven-day release.
Reservations are required "from late April through October". "Sixty percent of wilderness permit reservations become available by lottery 24 weeks in advance. Of these, any remaining reservations after each week's lottery become available on a first-come, first-served basis the Friday after the lottery application period closes ... The remaining 40% of reservations become available seven days in advance (up to three days in advance)." Confirmed on https://www.nps.gov/yose/planyourvisit/wildpermits.htm. Each weekly lottery, the Friday first-come release, and the seven-day release are the scarcity moments this target watches for.
Updated , checked by hand against the target's own page.
Watched from nps.gov, the target's own public page — not a reservation system we poll.