When I started doing overnights single handed, I'd set the timer for 15 minutes when I needed some shut-eye. Later on, I moved that back to 20 minutes. I've never been certain about what it's safe to get away with. I'm talking about busy areas off the east coast. When I crossed the Gulf west of Houston, where there's never any traffic, I slept for 8 hours. But what's the majority opinion for busier areas?