Well, seconds have been used since the Babylonian time period. However, we also don't know how carefully Harry measured the recharge time.
Wikipedia disagrees: http://en.wikipedia.org/wiki/Second#Before_mechanical_clocks
There are a lot of older units of time listed there, but none of them seem to fit.
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 119.
Plans for next chapter release:
There is a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)