I think it's a bit of a catch-22: given one of Putin's stated aims is to demilitarise Ukraine and remove Western weapons, NATO arming Ukraine earlier would have caused Russia to invade earlier.
Invasions take a lot of preparation. You can't just tell your army to attack some country - they need to plan exactly how they will do it, and practice.
The turnaround time on this sort of thing does not favor the aggressor.
The turnaround time on this sort of thing does not favor the aggressor.