significance refers to a measurement certainty about a number itself, especially its precision! and is unrelated to the magnitude/scale. the number and dimension "2.5634 mm" has more significant digits than the number "5,000 mm", though the most significant digit is 2 and 5 respectively, and least significant 4 and 5 respectively. this is true if i rewrite it as 0.0025634 m and 5 m. it does work for doing what you say in this case because a date is equivalent to a single number, but is not correct in other situations. that's why i said it does work here.

largest to smallest increment is completely adequate, and describes the actual goal here well. most things are ambiguous if you try hard enough.