Weight
There was no need to do anything fancy, so Zaos only made his squad train the same movements. Pick an arrow, nock it, and then aim. Zaos would be the one who would give the order to fire. So, they only needed to repeat those movements hundreds of times until they can do it in almost total synchrony. If Zaos had some time, he would have given them more instructions on how and where to aim. Still, since he needed to recover his mana, he decided to focus on his meditation. Even so, it was evident that he wouldn't recover his mana before sunset, much less before the next battle.
Despite that, Zaos still gave some instructions to his squad. The focus was for them to become fast enough to make each step in one second. Zaos heard that most decent archers can do that in a single second, while decent archer squads can do it in two seconds. That was why he aimed for that speed… even if it seemed a bit unrealistic.