Doesn't seem much, I know, and ordinarily, I probably wouldn't even notice.
Trouble is, Google Authenticator does, and it can generate "incorrect" codes when the clock is out (but "correct" given its understanding of the time at the point of request). This elevates it from a trivial non-issue to something rather critical.
I spent an age the other day working with Fastmail support trying to work out why I couldn't log in - they were baffled too, saying they use Authenticator, too, and have had no issues. It was only when the same problem occurred when I tried to use Authenticator for my Dropbox login that I Investigated further and discovered the clock issue.
Most odd, though. My iPad on the same network and also using auto-set for the clock, is spot on.
Anyone else getting this?