Jet erupts every 1 to 4 minutes during most Fountain Geyser eruptions. After Fountain has quit, Jet usually quits. Approximately mid-way through a Fountain Geyser interval, Jet often starts a new eruption series.
Fountain Geyser erupts every 1 to 4 minutes, Jet usually follows suit after Fountain stops erupting.  Jet often starts a new eruption series roughly halfway through the interval of Fountain's eruptions.