The tropical year — equinox to equinox — is 365.24219 days. That fraction is the whole history of calendar reform. Julius Caesar added a leap day. The Gregorian skip of three leap days every 400 years keeps the equinox from walking into July.
A year is also a map: perihelion in early January, aphelion in July, two equinoxes, two solstices. The documentary's torchbearer walks this wheel as if it were a temple floor.
Leap years are not a curiosity. They are the reason Christmas has not become a summer festival in the north.