How do you manage time and expectations at work?

I'm relatively late in a pretty successful career, but I find that I'm still doing heroic Hail Mary projects to keep my position safe and career alive. The sales manager in my head will reactively make some promise in a meeting with little thought, then I'll spend the next 3 months killing myself to follow through. It's worked so far, but it's getting a bit tiring and I don't think it's sustainable.

With such a deeply ingrained habit, it would help to get some ideas on how you all manage expectations at work to prevent digging yourselves into holes and keeping reasonable hours so you can protect your personal time.