You can feed all of the fruits in one go (it's one at a time so it will take a while but you can keep feeding even after message says feathers will change) however make sure to alternate between them occasionally so you don't go to the max end of one color spectrum (Red/Green/Blue) where further fruits of the same color alteration makes no difference.
There's also some RNG involves so be prepared to possibly need more fruit after the first attempt. You could of course also try and not feed it all at once and do most of it in one go, wait 6hours and check if it's the color you want then adjust accordingly if it isn't.