Select Menu > Settings > System > Clock.

Watch Face

Allows you to select a watch face design.

Use Profile Color

Sets the accent color for the time of day screen to be the same as the activity profile color.

Background

Sets the background color to black or white.

Time Format

Sets the device to show time in a 12-hour or a 24-hour format.

Set Automatically

Allows you to set the time manually or automatically based on your GPS position.