Hi again,
It sounds like the Breathe Reminders you're receiving are prompting you to start a session at different times throughout the day, and that time can vary day to day. We can further clarify how those notifications work. You set your Breath Reminders in the Watch app on your iPhone > Breath > Breath Reminders.
If you're seeing these reminders at unexpected times, it could be due to the reminder being rescheduled. "If you're moving or exercising, or if you start a session on your own, your Apple Watch reschedules your reminder. You’ll get the reminder a short time after you stop moving." The link we posted previously provides more details.
We hope this information is helpful. Take care!