12

Welcome to Strings_n_88keys!!!!!
And hey, since it looks like your start date is the same as Captain Atom, we now have a mode.
Mode - 6 days (mode is the number that appears most frequently in the group of numbers and since 6 is the only number that repeats that becomes the mode for the group.)

Strings, I went for a run and now your answer makes more sense. However, it is problematic. Here is why: it is impossible ever to sample a complete population. Every dataset comes from the representatives from the overall population who have chosen to participate (or who were recruited). So all data are samples of the population.

As I was trying to say, it all depends on how narrowly define the population--which probably depends on what your purpose is when calculating STDEV in the first place.

12