How the count works
The count is full days from your sober date to today, using your own device's date. On your sober date itself it reads zero. The next morning it reads one day.
Years, months and days are calendar time, the same way a birthday is counted. The one-year mark lands on the same date as your sober date, a year later, not after 365 days. In a leap year those differ by one day, and people notice.