I'm afraid you have far more pressing issues than how often you should be feeding
None of those fish (with the possible exception of the platy) can stay in that tank.
In a 'normal' set up, with appropriately sized fish in an appropriately sized tank, you should be feeding at least once a day, as much as they can eat in two or three minutes, but different fish need differing feeding regimens. Very tiny fish, like chili rasboras do better being feed twice a day; large ambush predators, like oscars, don't need feeding every day; three or four times a week works best for those sorts of fish.
In your tank you have the dilemma of needing to give the fish enough food (and, while alternate day feeding is recommended for fish in cycles, for the fish you have it's not a good, long term strategy) while also keeping it to a minimum to keep the water quality up.
Your fish should be eating quite a lot, as they should be doing most of their growth at this point in their life, but you don't have room in your tank for them to grow properly, so you're not really going to be able to feed them properly either
I'm afraid you're not going to be able to do your best for these fish until they're in a larger tank, either by upgrading yourself or rehoming the fish to someone else.
Sorry if that sounds harsh and not what you want to hear, but I have to tell you the truth for the benefit of your fish, and I'm sure you have their best interests at heart as much as I do.
