In the end, it's quite simple: the kernel doesn't accept invalid timevals. And negative tv_secs are invalid. It's that simple. If somebody gives the kernel a timeout from before the epoch, that somebody is being a total idiot. We know it's not a valid absolute timeout, since there's no way somebody is "waiting" for something that happened in the sixties. Yeah, yeah, maybe you're waiting for flower power and free sex. Good for you. But if you are, don't ask the Linux kernel to wait with you. Ok?
-- Linus Torvalds, Linux Kernel Mailing List, June 28th 2010