Linux-friendly PICs to timestamp an intermittent 4 µs long TTL pulse
Does it have to be specifically a PIC, or are you mentioning that because it was suggested? Any small microcontroller should be able to accept that signal as an interrupt (or even polled) input and count the number of pulses. Both the pulse width and the repetition rate should be well within the capability of most MCU's. The controller can then be interfaced to a PC via USB or other serial protocol to download the result.

You are right in that it is a solved problem. One solution is to purchase a datalogger that can read the pulses and timestamp them. Then the list of timestamps can be downloaded.

I have a similar off the shelf solution: a pulse counter board (normally used to interface flowmeters to PC's) with serial output. It will handle reading the pulses, but the logging and timestamping would be up to you. I don't want to turn this into an ad, so I won't include a link. However if you're interested in the off the shelf solution, contact me.