It actually plots the local time, i.e. a commit at 3am PDT and another at 3am EST would contribute to the same circle on the plot. (I did a clone of the old Git

It actually plots the local time, i.e. a commit at 3am PDT and another at 3am EST would contribute to the same circle on the plot. (I did a clone of the old GitHub graphs a while back.) So it isn't really useful for knowing when to contact faraway developers. On the other hand, it is fun to see how many committers are regular night owls.