Well, dude, we are shorthanded at the best of times, and I have been coming in 15-20 minutes early, at least, for the last few months, is what I should have said.
I had a boss get on my ass for being late. He said that the hours were there for a reason. I said okay, and started walking out of the door at 5:30 on the DOT. If I was on the phone, I said, hey, I have to call you back and I left. A few days later, I returned a message that he'd left (after 5:30)and he made a comment about how I didn't call him back that day. Then a few days later, he said "I stopped by your office last night and you weren't there" and I said "what time was that?" he said "oh, about 6" I said "I leave at 5:30" He STILL didn't get it. Finally, he had a project that he gave to me because "I know you'll finish it today" and I said "well, I might not, because I leave at 5:30. Hours are there for a reason". He finally got a clue that if he let 10 minutes slide in the morning, he'd get an hour or or so more at night.