ONK,
If you look up "timer" code through google maybe adding Borland, they have a true microsecond routine and can't remember but I think also nanosecond timer in C code. Looking though these functions, you will be able to see how the code works down at the hardware level and actually changes a few things around to make the ubiquotous PC offhand clock rate work precisely. If you are still in need of the source code email me at: wswain@hippag.com and when I get to work I can send you the C code files. Unfortunately, we have been off fortran for quite some time now so porting the code back may be left to you.
Another thought, look up IRIG time generator on Google as there may be some Fortran code out there for free (maybe?) that meets the IRIG time standard. This may be only to the 10th of a milllisecond or 100 nanosecond resolution.
Good Luck,
Bill