Widgets refresh on their own schedule. Opening the app or tapping the widget's check-in button updates it immediately; otherwise it refreshes within a few minutes and always at midnight.
Long-press the check-in button on a habit's detail screen and choose "I did it yesterday". Only yesterday can be fixed — honest streaks.
That's deadline mode: when you leave the app with a habit unchecked, a gentle countdown to midnight appears. You can turn it off in Settings → Deadline mode.
Only on your device. No account, no cloud, no analytics — see the privacy policy. Note this also means deleting the app deletes your habit history.
Settings → Restore Purchases, signed in with the same Apple Account you purchased with.