I have seen no confirmation since the merger but pmUA allowed
1) up to 12 hours on an international itin for SWUs/GPUs (note mileage upgrades were longer and hold thru a single stopover); and
2) up to 4 hours on a domestic /region 1 only itin.

So if this is still true, a >12 but <24 hours layover will not work.

Some previous threads
http://www.flyertalk.com/forum/unite...ts-needed.html
and
http://www.flyertalk.com/forum/unite...ns-thread.html