I always thought the 5 cm/s is a reference to the speed at which cherry blossoms fall to earth.
Today I was curious what the average speed of a human at it’s life is.
Didn’t even think of the anime at this time.
Found out the average distance a human travels in a life is 120.000 km. While the average time to travel this distance is 76 years (average age – baby time – unable to move time)
Guess what 12.000.000.000 cm / (76*365,25*24*60*60)s = 5.0033 cm/s
Now this whole “at what speed must I live to be able to see her again?” stuff starts to make sense