Like Russ said aquarium fish don't exactly use much energy unless they are breeding or being chased around by aggressive fish. They really dont need that much food.... small amounts 2-3 times a day is good. no harm in fasting them 2-3 days in the week.
Its much better to feed small amounts in the day then one large feed. They can only process so much and if you feed them a large amount once a day a good portion will just be pooped out and the nutrients wont be absorbed. Same goes for humans
Instructions simply saying 'Feed as much as your fish will eat in 2 mins' is just plain madness, those instructions have contributed to the death of many many fish. I mean feeding for 2 mins is fine if its the correct amount of feed... but people see this and plonk in large amounts of food for 2 minutes or just plonk loads in at once hoping the fish will eat it all in 2 mins... It depends on how they interpret the instuctions.... The feed amount depends on number of fish, size of fish and how energetic the fish is, temperature is a factor too.
Time doesn't matter so much..... Its all about the amount of feed! Just feed slowly so it doesn't all fall to the bottom which is kinda common sense in my book but people do still plonk food in the tank
The feed we use at the fish farm i work at has accurate instructions on how much feed to use for different weights of fish.... it also has instructions for different temps.
I don't see why tropical fish foods cant have a something similar... even if its like "feed x amount of pinches of food for x amount of inches of fish so everyone understands. I know inches isnt ideal as they would need to use a set weight for so many inches.. but most hobbyists out there are not going to weigh all their fish, i know i wouldn't