The res_timing_timerfd.so module should provide timing that is accurate as a res_timing_dahdi.so (provided by telephony cards). You can see what timing module is loaded into Asterisk by performing: # asterisk -rx "module show like timer" If you see that res_timing_timerfd.so is in use and is running, then you're good.
All
# asterisk -rx "module show like timer"
If you see that res_timing_timerfd.so is in use and is running, then you're good.