I had asked about this yesterday in a different thread because I had a similar question, but since I found this thread this morning - as an update, Alaska now lists 18 hours explicitly on their site
https://www.alaskaair.com/content/tr...e/checked-bags
If your trip includes more than one flight on Alaska Airlines and/or one of our airline partners, we will check your bags to the final destination on your ticket as long as there are fewer than 18 hours between flights.
If you will be in the connecting city for 18 hours or longer, you will need to claim and re-check your baggage. Additional baggage fees may apply.