Definitely minor to me. I voted for the first day you didn't shave. Actually, the first date you chose not to shave. That marks a conscious decision to grow a beard. You might miss a shave or several for a variety of reasons - illness, travel issues, etc. If you look at yourself in the mirror and think "Hey, that doesn't look too bad." and decide to grow a beard, then your decision at that point is the beard start date.
Since everyone's beard is constantly growing, your choice makes a lot of sense. In the end, the margin of error will be one day at most.