Because of the register being divided into 5 minute segments, yes. There could well be other uses as well, but it does replicate the first gun/second gun/start functionality of the Regatta.

Lots of Heuers have these divisions (Montreals, Calculators etc) and I doubt they were all intended for yacht racing, but I find it a convenient way to distinguish these Carreras from the "regular" Carreras. The other watches tend to either all have these markings (Calculators) or for the dial colour/model to determine it (e.g. Montreals), so there is less need to make that distinction - whereas contemporary Carreras come with or without.