Like PoJ said, it doesn't count unless you're actually in the grass. However, if there is grass or water in the area it will still advance a couple frames every 20 steps when the RNG checks for shaking patches, so your starting frame will still be shifted slightly.
Speaking of shaking patches, how would one go about RNG abusing a pokemon like Emolga? Is the pokemon generated as soon as the grass shakes? So that after I see a patch shake, it will always be the same nature/IVs no matter how many frames I advance?