If it were only a few days, I would skip it with the Bettas. I have understood that they can go for a couple of weeks without feeding. The danger of overfeeding a Betta is very real. If you have some small fish like pigmy cories or scarlet dario dario (who need live food, so I would put a good dose of live black worms or something) who are in danger of easily starving, then work something out. But for fish that can do without I would not take a chance on fouling the tank. I used them once. Some worked out, some didn't. I would use pellets rather than flakes where I had to use them. The flakes jambed up and didn't despense.