Lemmy does exponential backoff with something like this:
retry_in = min(1.25^retry_count, 24*3600)
Basically, the timer for the next retry will grow exponentially until it reaches 1 day, then it continues to retry every day.

By that time, about 5 days will have gone by going through the previous retry failures.

If will eventually give up and mark as dead but I don't remember the threshold for that.