My understanding is that with the Declarative Beacon API, if a page is kept in the bfcache for an extended period of time, it's still eligible to send the beacon once the page is evicted from the bfcache, which might be a long time after the user has navigated away from the page.

Would it be possible to instead send the beacon for bfcache'd pages after they've been in the bfcache for a minute or so? I think the page would want to check when waking from the bfcache to see if the beacon was already sent or not (by checking the state field of the beacon from the explainer) -- if it's already sent, the page may want to create a new beacon (at its choice).