i guess that depends what its decent/good/great for you

i compare speedrunning to solving rubik's cube the fastest you can

after reading a guide up you can solve it no problem, and you will be much better than most people already (who have never solved/speed ran)

then as you get used to the strats/guides you start slowly dropping your time, but consistently and big chunks of time

but if you wanna be REALLLLLLY the best or "at the top" you will put weeks of time just to drop a few seconds at most

it also of course depends on the game and how many hard tricks there are or the duration of the game, but you should see some quick progress early on