What’s the full sleep data, or at least the variance? 31 may be large enough. And if it’s not, getting more by the end of the year may not make a big difference. Power only increases at the square root of the sample size.
But its one of the more annoying experiments to let a coin decide if you have to take another walk :) So I'm not sure how often I will do that. I'm pretty convinced already that walking more is a good thing.
I'm in a hurry right now, but I will probably write a full blog post about the steps-sleep relationship with p values and everything some time next year.