Actually . . . two weeks is not too long in some cases. I have 20 (SMALL) freshwater fish who have gone three weeks on just one of those "slow-dissolve" Feeder Blocks dropped into the tank at the beginning. Everything was fine when I returned home. (Of course, the tank also has live plants on which some algae collects and were probably useful to the Corys, Guppies, and the Otos.) Tetras and Glowlights managed with the block.
Disclaimer: I wouldn't recommend the "feeder blocks" as a rule, but - in a pinch - these are OK.
Ended up being able to arrange for the lady who cleans the school over Spring Break to feed the fish every other day. Felicia's teacher will also let me in once a week to top off all the tanks and give all the fish a feeding of frozen foods as a treat.