Most good ideas are obvious in hindsight. ;) But AFAIK, Google was the first to do this live and in production by hacking NTP, which is (apparently?) the same as what Amazon is doing.
What if in a dst jump. It had. Pay namrog84 $100 at 1:30am. Then 2 rolls around and it's 1am again and now I get paid a second time. Win! But if dst was smeared over a day. This would be easily prevented.