It can be as tough as you let it be. Amazon seems to be a place where I could be an average worker (9-5, just do what I'm told) and easily last for a year or two without being fired. Or, I can drive forward and keep asking for larger and more varied problems to help round me out as a developer.
On my old team, we showed up around 10, took an hour to an hour and a half long lunch, and then left around 6. Some people had different hours, but most of us rolled in and out of the office around those times. We still worked hard while we were there, but when we were burnt out, we went home a little early with no bad feelings. There were times of stress, but you never felt overwhelmed for that long.
On my new team, most of us work from 8am to 6 or 7pm. We're always trying to keep up with what's asked of us and it's very exhausting. Every team is different in Amazon, and they stretch to both ends of the scale. My advice is to interview your future team before you accept the offer (if allowed). Ask about work hours and their priorities / backlog. If you just want to make it in to the company, there's still the company-wide policy of suggesting that devs who are unhappy with their teams after 12 months switch to another team. Depending on where you're at, relocation benefits are included, and team-switching is a widely-accepted thing.
