Never had someone snitch on me before at a job until now and it shocked the hell out of me. It was about me not being on time. What the **** is this middle school?
I would have done the exact same thing. If I am expected to be on time, then YOU need to be expected to be on time.
I'm the Department Steward and we had to deal with a chronic timeliness issue recently. WE (the other members of the Department) brought it up to our Supervisor (who was already aware).
You have an accepted start time. Be there at that time. Very simple.