This appears to be your first post to the forums, Welcome!
These points-only deals have been coming out once per day during the week most recently. From what I have read on the forums, the deals are offered at a random time each week day. I have only found the randomly offered deals because someone posted to the forums that they one was in the catalog or I personally saw it in the catalog before it was sold out.
In addition, more points-only deals have been offered on the first day of each month with the monthly "Extra Credit Rewards" program. The best deals sell out the first day, some within hours of the beginning of the month. There is an Extra Credit Tab on the Redeem page that has a link called "Learn more about Extra Credit Rewards" at the following: https://www.aarp.org/rewards/redeem/extracredit/