I also has a sked change into JFK. Only around 40 minutes but gets me in closer to midnight into JFK versus just after 11pm. This late at night, it does make a difference and now I'd rather just do the red-eye.

DL used to be pretty flexible on sked changes but now they seem to be tightening up and I was told absolutely no waiver of change fees (I have a P class fare so there is a change fee) unless the sked change is 91 minutes or more.

Not sure if I just got unlucky with the two agents I spoke to but both said absolutely no ability to change flights with repricing and paying change fees unless sked change is 91+ minutes.