When I load a StackExchange site, the questions on the main page show up with timestamps like "answered 5m ago joeuser":
But after a minute ticks by, all the timestamps get recalculated and are shown with different abbreviations for the time spans (like "answered 6 mins ago joeuser"):
The new lengths often cause the page to reflow like something meaningful has been changed.
Is this a (very small) bug, or is there some good reason for it?