Am I In The Wrong? Boss Got Mad Because I leave 2-3 Minutes Early?

I'm a mechanic and I work four 10 hour shifts from Monday to Thursday. My shift is from 6AM until 5PM, however I usually clock in at 5:57AM to 5:58AM and get right to work as it takes forever for the computers to boot up thus causing a delay in me clocking it. At the last half hour of shift everyday, all the employees clean up the shop (sweep, pick up trash, etc..) once that finishes, majority of us sit around on our phone, talk, and wait to clock out. Majority of us also clock out a minute or two earlier as well and have been doing so since they've started working here. For some reason today my boss singled me out and asked if I knew we worked until 5PM. I replied with "everyone else is leaving as well". He asked me if I was going to do the same. I just told him I'd stop doing it for the sake of not arguing. Was I in the wrong? Wouldn't it be worse for me to loiter on the clock (stealing time) and go into overtime? I did my 10 hours so I don't understand. I've also been doing this job (7 months ago) since I've started but only now it is an issue? He also didn't say anything to anyone else that did the same, not to mention how some employees are chronically late.

Posted by /u/SupremePizza123 on r/jobs
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