Change the start hour of a workout
Choose device
From Desktop/Laptop
Click calendar under tracking, then press the "day" button on the right side. You can change the day by clicking on the right and left arrow buttons on the left of the page. when you get to the right day, drag and drop the workout to change it's start date.
Using the App
Click the bottom "calendar" button. then select the day, and the workout you want to change. A popup will appear with details on that workout and, to the right of the date will be a little blue clock icon, click on that to change the start date and time for the workout.