Correct, it was still 2 PM, but Jenkins thought it was 2 PM on a day that he’d already worked.
Jenkins was planning to go to bed on Wednesday the 28th at 10 PM and had his next alarm set for 6 AM on Thursday the 1st. He then adjusted his clock back to Tuesday the 27th at 10 PM, planning to sleep 8 hours plus the entirety of the “extra” Wednesday.
When DST ends you set your clock back 1 hour (or it does it automatically nowadays) in the middle of the night, gaining 1 hour of extra sleep
The joke here is that the guy did the same for Leap Day, setting his clock back 24 hours and gaining 24 hours of sleep, so when his boss called at 2pm he was in the middle of his ~32h night
It didn’t become 2 AM. It was still 2 PM, but on a day that Jenkins already worked.
Jenkins was planning to go to bed on Wednesday the 28th at 10 PM and had his next alarm set for 6 AM on Thursday the 1st. He then adjusted his clock back to Tuesday the 27th at 10 PM.
But that's not a good joke, IMHO. It strains credulity even in the context of a comic strip and is so counterintuitive and unrelatable that no one here was in the cartoonist's head space.