Darrel,

Well, Me being Me I want it to do EVERYTHING, so the distance between the gates will be an input variable.
My light source is a beam-split 650nm (red) solid state laser that's way more powerful than it needs to be (but also a lot more fun!)
My Optical sensors are Osram SFH 5840 PhotoTransistors with built-in Schmitt Trigger.
The outputs are combined into a single pulse using an LS74F00 configured as an S-R Latch. (this allows me to use the same code and input pin with either one or two sensors)

The timer code is based on DT_INSTANT_INTERRUPTS running on a PIC18F4680 @ 20 MHz

This is all working very well as a high resolution timer, though I am still working on some corrections for software and hardware delays.

I may consider redoing the timer portion of the software using the N-Bit Variable Math, as I'm currently limited to about 1.5 Minutes.

I needed the N-Bit Math to get the resolution I want when converting from Time to Speed, as I end up dividing two large numbers.

My immediate goals are...
How fast are Pinewood Derby Cars?
How fast is my dog? (Very Fast!)
How fast am I? (Very Slow)
How fast can I back-slap someone? (approx. 29.97235 MPH)-DONE!
What is the muzzle velocity of my air rifle with different pellets?
How fast does that Jerk down the street drive past my house while kids are outside playing?
...

I only have time to work on this late at night.
I'll work on cleaning the code up a little before I lay it out for all to see.

So far this has been a really fun and educational project.
My youngest daughter (11yo) is learning with me, she seems very interested in what I'm doing. So I try and explain it to her as I go.

Again thanks to you and the others on the Forum that are so willing to share your knowledge to help others learn.