Slow-mo formula can't use timeframes, it uses speed explicitly. And slow-mo formula uses more assumptions, true, but they're considerably more reliable assumptions to choose from, as many of the aspects rely on usable IRL metrics, like shockwave speed (Explosion speed calculator could make it more accurate but link is dead) and the apparent speed used (Walking speed for viewing those objects in slow-mo).
Things get even worse with anime adaptations where you straight up cannot use any of that, you'd have to rely on how many pixels the "measuring stick" object moved, like with most slow-mo calcs involving actual cinematic footage (Like Quicksilver punching Captain America, Raiden slicing a Boxer in half, Wondie deflecting a bullet, etc.)
Garou situation was locked to Earth's atmosphere, but with Io, they have considerably more ground to cover and it's already a massive leap compared to what he did against Golden Sperm, so using those reaction speeds for him here would be wildly inaccurate.