What distances is it going to be used at?
For times in the picosecond to hundreds-of-nanosecond range and low rep rates, a "Time to amplitude" converter (basically using a capacitor as an integrator) followed by an ADC is very simple technology. Dates back to WWII radar and probably earlier. There are gotchas with switching the current source on and off rapidly and resetting the capacitor back to zero charge, but these are lessened somewhat when you are in control of the repetition rate/sync.
For longer times, a combination of a counter with a TAC is very appropriate. The counter won't have to run in the GHz if you do it right.
There are some clever things that can be done with multiple-approximation switchable delay lines, too. Not very hi-tech (this would be the solution from 40 years ago) but it does work if you control the repititions.
All that said, I would highly encourage you to look at the waveforms on a scope before going into too much deail with measuring sub-nanosecond times. You'll have to work with discriminators on your sensor, for example, and adjusting their threshold depending on path loss (I suppose for very short paths this may be a non-issue, the laser rangefinding I did was in the several km range) or adjusting laser output power to compensate for path loss.
Tim.