You're partially right for the case of trilateration, usually these would be placed about 10km apart with a GPS PPS clock (at least) and would be using sensors with a much faster response rate.

With triangulation you only need the clocks accurate enough to correlate the events. This will largely be determined by the rate you see events, and you only need to distinguish specific events if you want to differentiate locations of individual strikes as opposed to a storm front. For a boating case you probably only care about the location of a storm front.

Two sensors measuring angles from a couple dozen meters apart can get you a pretty precise location of storm front especially when aggregating results from multiple detections.