With the reaction time locks, you can just save beforehand and try again. I messed up a few times until you get the rhythm. Heck, you don't even need to do all of them, they're just loot boxes, and the loot system in this game is annoying as hell.

I can't give you sniper advice, because I never played as a class that could really use snipers effectively in ME 1, 2 or 3 (Vanguard, Adept and Sentinel). I'm not great at sniper rifling, and the thought of concentrating on headshots while under fire is... perturbing.