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. If your group counts the sober date as day 1, switch the count and every number moves up by one.
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. A sober date of 29 February is marked on 28 February in other years.
Hours are full days times 24. The page does not ask for the hour of your last drink, so the 24 hours mark is the day after your sober date.