Venus GPS 1PPS configuration
I contacted SkyTraq directly, and they said:


  [The Venus634LPx is] a very old product that does not [support the] precision timing related functions you ask [for]. You might consider this instead: http://navspark.mybigcommerce.com/ns-t-precision-timing-frequency-generation-gps-receiver/


So the options in my question is not applicable to the Venus634LPx chipset. The device they suggested uses the Venus822A chipset.

Still no answer about what these "precision timing related functions" actually mean.