The flash accelerates at 0.05 e/f^2 to a maximum speed of 3.5. So it needs 70 frames [2.333 seconds] to reach full speed, yes?
Yes.
Time to divulge a little secret though: in older Spring versions (those where the "pathing" was considered "good") the acceleration and brakerate tags were actually interpreted
incorrectly, with the effect that units could change their speed
much more easily than what was supposed to be allowed by the raw tag values. More recent Spring releases however
do implement the physics the right way (effectively giving units more inertia, combined with
proper turninplace=false behavior) so players whine about there being "less control over units" and "declines in pathing", yet at the same time they think setting values that better reproduce old engine behavior (which is what FA's proposal comes down to, not that he had a clue) will "change the game into something else" and "is not a solution". This is why their opinions are
worthless to those in the know.