Faster but later

All clocks in movement (relative, compared to us) are in retard, according to the formula

where t' is the time as we observe on the clockin movement and t on our (at rest) clock
This is simply because in movement the light-ray reading the clock position has to go a longer, triangular way, like on the picture below. And the light travels always at a constant velocity.

The ray sent perpendicularily comes always back, independently if it is sent at rest or in movement

                 See the same from a perpendicular direction

see also the detailed calculation