I think there's a range of ways you could communicate it. Kind of depends on the structure of how the backlog gets churned through. Maybe each episode card includes a sigil for the transcript that's either a green circle with a check or a short summary of how long you expect before you process it (6d, 6h, 15m, etc)? That's also kind of busy - maybe you end up putting a single element at the top of the podcast page saying how long before the next episode will be transcribed and perhaps how long before all episodes might be transcribed (i.e. you need to wait at least this X long and probably not longer than Y)?

Having a big central page for all backlogs sounds cool, but I imagine I would probably care about the expected delay for a particular podcast / episode of a podcast most of the time?

Suggestion, you've probably fairly easily got access to how long the most recently completed task took?

Perhaps on the submission form include a low-resolution indication of that, so people's expectations are set before they enter a podcast link? Round it off to the nearest minute/hour/day, and format it appropriately:

"Processing times are currently around 3 hours"

or

"Processing times are currently around 17 minutes"