This looks like an answer to my question I posted elsewhere under this story. (Namely, how do I get egg-timer elapsed time since a certain UTC time? Which, the UTC component isn't a must have for me, the Unix Epoch will work just as well.)

But I notice that your solution is POSIX only. How about Windows?

And how do NTP adjustments affect this solution -- surely when the NTP server tells you your system clock is consistently off by 16%, there's got to be some effect on clock_gettime with CLOCK_MONOTONIC, right? I'd like to retain the ability to use NTP to improve the accuracy of the results.