Hey Georgia, welcome!
As far as I'm concerned, the flake manufacturers would very much like you to feed your fish that much so they make plenty of money.
I usually only feed my guys once a day, and I certainly don't give them "as much as the fish eat in 5 minutes" (what the stuff I have says on the can). I'm not sure how reliable it is, but I have heard that a fish's stomach is (usually) of similar size to one of its eyes, so really, they don't need heaps of food. Also, flakes swell up inside and fills them up, but if they get overfed, they can get intestinal blockages, which can cause some grief. So, feeding amount - keep it to a small pinch, because there's often much more there than there looks to be, and if the flakes are fairly large (ie. if a flake hangs out of a fish's mout before they're able to swallow it all), it's also worth crushing it a little. It shouldn't take the fish like 2 seconds to eat all the food, but they sure shouldn't be feeding for 2 or 3 or 5 minutes, ether - maybe 30 seconds. Just make sure they eat it all, and it doesn't sink to the bottom and pollute the tank. If you prefer, you could also feed them smaller quantities twice a day.
On a slightly different note - your fishies will love you if you vary their diet every once in a while. Algae tablets/discs/pellets will be happily eaten (usually only put one in at a time, unless they're tiny); also frozen peas (with the outside skin removed), lettuce, spinnach (plant these in the substrate), and veggies like zucchini and cucumber (both skinned, deseeded, and half-blanched). Feed them this kind of thing once or twice a week, and just experiment and find out which of them they like best.
Hope that helps a bit - by the way, this is all my *opinion*, and somebody else will probably have better advice for you
Happy fish keeping!
