Sometimes you can't accept. It's happened to me before. I'll queue in DF and then change jobs and go off leveling something else, usually in a FATE. The timer comes up when I'm engaged in combat. Precisely when you're not allowed to change jobs. So I'll either try to get the kill real quick, or disengage and try to run outside of range of the mob so that I can change jobs. I change jobs, go back into DF... only to find the timer's expired and I have to re-queue.

It happens.