2) Assume you're going home at 5:30, then plan your day backwards.

Work will fill the space it's given. Give it 24/7 and guess what happens?

You need boundaries if you want work/life balance. But this also helps you work better because it forces you to be efficient.

By setting a deadline of 5:30 and then scheduling tasks you can get control over that hurricane of duties.

Cal calls it "fixed schedule productivity":

Fix your ideal schedule, then work backwards to make everything fit — ruthlessly culling obligations, turning people down, becoming hard to reach, and shedding marginally useful tasks along the way. My experience in trying to make that fixed schedule a reality forces any number of really smart and useful in-the-moment productivity decisions.

What does research say prevents you from getting burned out at work? Feeling in control of your schedule.

Great advice.  I think I need to plan to finish my day by 3 PM (since I often need to pickup the kids), to make absolutely sure I'm working on the highest priority items for my startup.  Rather than just creating content for your startup! :-P

Good point. Make sure to do the most important thing first each day.