March 24, 2021 Lottery results published
April 1, 2021 Reservations open for remaining dates at 7am PST
April 30, 2021 Deadline to confirm awarded lottery reservation and pay reservation fees
May 1, 2021 Dates from unclaimed lottery released for web reservation at 7am PST
So, basically, you can start checking rec.gov April 1st at 7am for any permits that weren't awarded in the lottery.
Then May 1st at 7am, any permits that weren't accepted and paid for will go up for grabs.