Joe is Vanguard's global chief economist and head of Vanguard Investment Strategy Group. He's also a member of the senior portfolio management team in Vanguard Fixed Income Group.
Apollo missions took about three days to reach the moon. But the quickest trip to the moon was the New Horizons probe, which zipped past the moon in just 8 hours 35 minutes on its way to Pluto. However, the spacecraft didn't even slow down or approach lunar orbit. Tidal forces.
Since the full cycle is about 29 1/2 days long, we can say it is approximately 4 weeks long (plus 1.5 days). So it takes a week to go from New Moon to First Quarter. Another week to get to Full Moon. And one week to get to Third Quarter and finally one more week to return to New Moon. New Moon and Full Moon are two weeks apart roughly with only about 3/4 day extra to add.