Reach gives you raw data (UBX files). It can also convert that to RINEX data (OBS, NAV files). With RINEX data from base and rover, you perform the post-processing. The output of that is your position data (POS files), and if you captured events (with hotshoe adapter), then you will get a event data (_events.POS files).
Once you get have that _events.POS file, then you can look inside it for your the time marks that were triggered by the hotshoe adapter.
That is as far as I can take you 
@wizprod can probably do much better