macOS Accurate Timer

http://developer.apple.com/documentation/Cocoa/Conceptual/Timers/Timers.html
for the cocoa way of doing things.

open a terminal and run:
man localtime
(others will get you to the same man page)
for the Unix way of doing things.

Both should work, though perhaps not to the precision you need. You should look into both first, though, because they may do what you need.

-Lee

mach_absolute_time gives nanosecond precision in 10.2 and later.

as an aside, in the abscence of a real-time OS whose scheduler can guarantee a process CPU time with very strict constraints, this is all for naught. Your process could be preempted immediately after any call giving you some sort of nanosecond precise timing. By the time your next instruction runs, the sampling, timer value, etc. may be woefully and misleadingly out of date. I don't wish to discourage your efforts, only get you thinking and temper your expectations.

-Lee