>>13535914they are not time units though, they are natural events that happen in almost exact periods of time (however there is significant variance which makes them invalid as scientific units)
in the last 20 years we've had a ~20ms range in variation of length of day
tidal effects are supposed to be the main reason for these variations
length of the year is believed to change less in proportion, but still the proximity of other planets can still create measurable changes in the speed of the Earth around the Sun
