Good evening dear athletes - unfortunately I can't give you any (precise) information on this because my cardiologist advised me not to wear the Garmin Vivoactiv for the time being. - I was therefore not able to check out the Garmin properly.
However, I seem to remember that the time is NOT continuously displayed (for energy reasons!) and is actually activated by 'wiping' and/or hand movement.
MfG - Kurt

The time is always displayed. In the dark, however, you have to tap the touch screen for illumination.

You can set whether the time is displayed only by a gesture or continuously.