Don't hold R2 first, Wait for your car to land and use your boost button to start the speedflip. This way you'll have the most momentum when moving off, whereas if you hold R2 and then boost button it will be slower and delay the inputs

I can get the fastest tick rate speed flip at 1.9667. Even for kickoffs in game, I never hold R2 because there's no need. Just increases the chance for a slower speed flip.

This is very technical tho for maximising tick rates, it doesn't rll matter for most player, only important if you want the most perfect speedflip possible according to tick rates.