My yesterday experience:
Tried to standby an early flight but did not get it despite ranking No. 1 on the upgrade list. The gate agent said he would not give it to me because I got a confirmed J seat in an later flight and he would give any seat, including J seat, to those who did not have a confirmed seat first. Not sure if it should work like that, but in the end the previous flight was delayed so much that I just took my original flight anyway. It was supposed to arrive about 3 hours before my original flight, but in the end only about 40~50 minutes earlier.