Can I break a betta food feeder in half? I have a 7 day feeder but I will only be away for 2-3 days.
You can break these up but remember that if it's one you apply to the glass, you'll need enough surface area for it to stick. I've done this before with the smaller tropical tabs for shrimp and as long as there is still enough flat space to stick to the glass it will be fine.
I'm sure you already know (but it's worth saying for future visitors) - these types of food can be problematic in terms of water quality. Owing to the fact the food is exposed to the water for a prolonged time, you can get a build up of ammonia as the food starts to decompose (often accelerated by the water temperature being raised). It can also lead to some fish overeating because a lot of fish will eat any food available regardless of the damage it could do to then.
I agree with Karl Richter - your fish will not need to be fed every day (unless you're aggressively attempting to make a discus put on weight or something). A lot of fish keepers will overfeed their fish because they look hungry. As Karl also pointed out, in the wild, a fish is unlikely to feed every day without fail. I've personally left my tank (180L tropical community) for just under a week with no food and they've been fine. They nibble on algae and plants (if you have any).
This is an interesting video about preparations for leaving your aquarium which might help you feel more comfortable with the idea of not feeding your fish.
I guess you can. It's not important. Did you check the wrapping? Fish can remain without food for 2 or 3 days. That's probably why the feeder comes for 7 days and has no break lines. 1 day per week and 1 week per year without food is recommended because it is natural for fish to not find food every day and motivates them to eat algae in the tank. They probably have a feeling of hunger, but they don't starve and adjust their body size after longer periods of absence of food.
Your betta could survive not eating for 2-3 days since normally they are fed every other day at pet stores. Feeding blocks are great if you have a bunch of fish in the tank and awful if you don't. They create this fuzzy residu on the bottom where your gravel is that is a pain to clean and since it is food, anything that is uneaten can cause ammonia levels to rise.