Any hour worked in EM is equal 1.5 hr doing anything else. This is an undeniable truth of Emergency Medicine. Newbies just refuse to believe it and therefore get burned playing with fire. 30 hr per week of EM = 45 hr per week doing anything else. Refuse to believe it and get hurt. I've lived it. Every one of the 15 hours you can't imagine would be filled with anything other than starting businesses, goofing off and enjoying life, is spent recovering. It's true. Know it. Live it. Learn it. Or get hurt.
That being said, can you practice EM and start a side business? Sure. But no easier than a banker, or a family physician who works 45 or 50 hr per week.
Trust me. When you get off a 6 pm to 4 am shift, finally get home and get in bed at 5:30 am, wake up at 8:30 am unable to sleep any more with the sun blaring in your eyes after 3 hr sleep, you won't want to start a side business. You'll want nothing more than to put on eye blinders and go back to sleep. Add to that, the fact that the the 32 hr EP work week isn't even real for most EPs. Due to the EP shortage that has no end in sight, most end up working much more and pressured to do so, ad infinitum.
The 32 hr EP work-week evolved not for sh-ts and giggles. It evolved as a means of survival. EM is one of the, if not the, toughest speciality in all of Medicine. Free advice. Worth gold. Cash it in.