The issue here isn't how many hours people can work it's what stress level can you personally handle and how you can personally handle stress.
Focusing on reducing debts is great motivation to suck it up for a while and work your butt off but if you neglect other areas of your life while attempting to fix that area new problems will arise bringing up the stress. More importantly if you're working long hours you need an instant stress relief to kick in when you leave the job, sitting down and watching TV, or sleeping, will not do that, failure to pay appropriate attention to that area will result in health issues, guaranteed. Stress is a physical reaction, not a mental thing and it needs to be counterbalanced by something that turns off that instinctive stress reaction, personally three things work for me: Physical exertion, something relaxing and grounding like Tai Chi or yoga, or reading a book in a cafe (as an extrovert the people surrounding me energise me), know what works for you and you'll know what you can do.