Typically, I use the N-of-1 method with another biomarker (vascular age, derived from PWV) which you only measure once every day. Since it is the number of data points that determines the reliability of results, it is best to have at least 14 for that biomarker. For blood pressure, which you measure twice or more per day, a week of measurements is reasonably sufficient. Of course longer observation periods are better. I can't program the flexibility of adjusting periods into an Excel file. I have those degrees of freedom on our LiLo research platform, though.