Just do normal stuff with it for 10 days then make a return decision. You won't get any better test. If you want to be really keen then make sure you use all the ports but "burn in" testing isn't necessary...you end up convinced the battery life is poor, fans run all the time, CPU is busy and causing lag...
I think the days of letting a computer run an app for 24 or 48 hours to "burn it in" are long gone. Apple does its own burn in, and the best way to find any short comings is to use it as you normally would - just my $.02
I personally think you're wasting your time. If any problems arise, they'll show up with normal use. If they do crop up, you have a warranty, I advise you to use it, it's the reason it exists.
You are definitely wasting your time doing this. Apple already does their own burn-in at the factory. You don't need to repeat the cycle.
Also bear in mind that if you do any "burn-in" testing that involves storage writes, you are absolutely doing more harm than good by intentionally shortening the lifespan of your SSD.