Earliness: the quality of being early
Solution 1:
Timeliness or prematureness are probably too vague and spurious respectively.
Could I suggest removing the constraint that it is __ness and suggest "spring doesn't mind being an early bird," which might even have some pleasant connotations if spring is what is actually being written about.
Solution 2:
I like earliness best, but if you don't mind being a little on the fringe, you could try prepunctuality.