If an activity is displaying the incorrect time you can correct this issue via the steps below. Select the platform you are using:
Open the Garmin Connect app.
Access the menu by selecting More (bottom right).
Select Activities.
Select All Activities.
Select the activity you want to edit.
Select 
(upper right corner).
Select Edit Activity.
Select Time of Day.
Edit time and select OK.
The activity should now show the correct time for your activity.
Sign into Garmin Connect from a personal computer.
Select Activities from the navigation bar on the left.
Select All Activities.
Select the activity to change.
Select
(upper right corner).
Select Edit.
Select Time to edit start time if desired or click Time Zone to edit if desired.
Select Save.
The activity should now show the correct time for your activity.