the evil hour/day/moment
the evil moment/hour/day
The moment, time, or day when one must do something particularly difficult, unpleasant, or stressful. I knew I had to start filing my taxes soon, but I've been doing everything in my power to put off the evil day. Having "the hair of the dog" may make you feel slightly better after a night of heavy drinking, but it's only postponing the evil moment when your body's hangover eventually kicks in.