How long do stories remain on the "up for archival" list before disappearing?
Not sure. You should contact our host directly using the contact link on the SOL home page or post in Bug Report and Feature Requests to get his attention more quickly.
Mostly it's 7½ days, but sometimes it's 7, so work on 7. Archive checks (adding stories to the TBA page or moving them behind the paywall) are done at 05:30/17:30 GMT/BST, sometimes an hour earlier (I think to make daylight savings transitions easier). SOL, FS and SFS archive checks all take place at the same time, so you can work out when the checks take place by looking at one of the other sites, adding on the number of hours to the present time, and taking the 'half-past' before that time. Sometimes when there are a lot of stories added to the TBA page, they stay up longer (possibly so basic members can visit all the stories before they go), however I think the subsequent authors being archived do not have any allowance for the archive list being very full so the go at the 7+ days. If a story from an already-archived author is added by the site staff (rather than by the author, which would cause them to be not-archived) it only stays on the TBA page for ½ day; this has happened recently. If a story has multiple authors, it never appears on the TBA page, just goes directly behind the paywall when the last author comes up for archival.
Typical case:
06/04/2020, AM check, OldSpice added
13/04/2020, PM check, OldSpice removed
7-day case:
02/04/2020, PM check, wendyw added
09/04/2020, PM check, wendyw removed
Already-archived case:
11/04/2020, PM check, Katie McN has one story added to TBA list (26 more already archived and premier-only do not appear)
12/04/2020, AM check, Katie McN has no stories on TBA list (all 27 premier-only)