Clocking in on time and checking out mentally at minute five still counts as late.

Being present and being there are different, and only one of them gets the work done. Arriving on time is the easy, visible half, and the harder half is bringing your attention with you, which nobody can see on a timesheet and everybody can feel on a shift. Drifting out early is a quiet kind of lateness that is hard to challenge, because the clock says you were there. Your coworkers know anyway.

Try one shift where you decide to be fully in it from the first minute. Phone away, next useful task found, people spoken to. Compare how fast the time goes against your usual.