Heh, when I was messing around with the sorting in December, I had wondered if anyone actually used absolute time for correspondence, since it seems pretty impossible… I guess the answer is “yes”, and “yes it’s pretty impossible”.
The same problem exists for correspondence games using Canadian time. Canadian time is great for in-person games. It’s designed for adapting a standard analogue chess clock, which is absolute time, to time-per-move. But for online correspondence games, if the clock says “3 Days”, that might be for 1 move or for 10 moves (configurable up to 50 on OGS), and you can’t tell just by looking.
TBH, it seems like the “right” solution is to stick to Fischer, Simple, and Byo-yomi for correspondence games, since they all work pretty well for that 
… but I wonder if it would be reasonable to augment the display of the clock when shown in game lists:
- For Canadian, maybe a move counter, like “3 Days ⑦” for 7 moves.
- For Absolute, maybe
!⃝, like “3 Days !⃝”, to represent “all the moves”.
WDYT?
(The sorting idea you propose sounds possible too. I worry about straying too far from “expiration time”, in case we trigger more instances of thumbnails jumping around, but maybe it’d be fine. I don’t think it makes sense to add as a setting, since it’s so specific/fine-grained.)