Accurate Timer, follow up and How to?
My suggestion on where to start is by understanding time and the fractions that time is usually broken down into. Your answer to my comment about the real need for 100ns resolution is this: -


  Yes 100ns resolution. This would allow for rounding to .001 seconds
  and make sure that the numbers were beyond doubt (you would be
  surprised how excited 2 parents get when the time shows the same for 2
  cars but one is declared the winner). I have a track for testing and
  can put in place all the electronics and a dedicated PC to do the math
  and formatting from the timer information



1 whole second is 1000 milliseconds
1 millisecond is 1000 microseconds
1 microsecond is 1000 nano seconds


100ns is 0.0000001 seconds - you want 100 micro second resolution and may I also suggest you buy a modern calculator.