The hours weren't generally that intense with that job (and fuck it, going to come right out and say who it is: Nielsen Media Research), but the pay sucked ($30k/year in the Baltimore area is NOT a livable wage), the conditions were awful, and my supervisor was literally the worst human being I've ever had the pleasure of meeting. One of my first experiences with him was him berating his wife over the phone. That should have been a sign that I needed to GTFO, but it's amazing what you'll put up with if you need to try to hold down a job.
If nothing else, it helped me get better at standing up for myself. From that point forward I've been far more apt to call managers and supervisors out if they try to pull a bunch of bullshit.
I did kind of get the last laugh, in a way. This guy disliked me to the point that when I put my notice in, he told me to stop working immediately, so I behaved myself and did as I was told. I didn't organize anything, I made no records of my last resolved calls, and I basically just plopped everything as-is into the boot of the piece of junk company car that they assigned me. I hope that pissed him off.
And yet I still can't imagine pulling 15 hours a day, 7 days a week. That's like perpetual crunch time. I've had periods where I was pulling 10-12 hours a day for 7 days a week, but that extra 3-5 hours makes a huge difference. I guess it all comes down to how much you enjoy what you do.