I recall being in college.. there often isn't much time. I lived at home though, so I managed to keep my horse and my fish and turtles.
So I take it there are no sources to buy adult brine shrimp locally ? Luckily for me, one of my lfs
's stocks adult brine shrimp. New stock every two weeks, rarely last more than a few days. I'll buy one portion, which will last 4-5 days, give or take. I dip some out with a fine sieve and swish them into tanks where they'll swim for some time, though most end up near the bottom. They never last long - feed them to all my fish when I have them, as I do blackworms.
If you can get live blackworms, they'll last a LONG time in the fridge - up to 4 weeks, or more. Available online too. They'll do fine in an open 32 oz deli cup. [If you have to cover them be sure there are lots of air holes ]. The one thing is, they must be rinsed daily so their water won't foul.
A chopstick is a perfect tool to gently swirl the worms, and usually some will wrap onto the stick. I hold the stick over the tank in the same corner each time and the boys come up to snatch them. Those that sink are eaten later on. Bettas may not be designed to bottom feed but they have no problem doing it for live foods.
If you have any space at all and can get some, scuds are another live food that Bettas appear to really enjoy, and take virtually no effort to culture. Available from labs like Carolina Biologicals if you can't find some wild ones under a rock. Sometimes they show up with plants, that's where mine first came from.
Even a gallon size plastic jar or vase with plants and a bit of substrate would serve to keep a scud culture going. Kept in a bright but not overly sunny window, such a culture won't even need lighting using lower light plants. Feed a bit of algae based fish food every few days or when you see it's gone, as scuds will eat plants if they get too hungry, though they prefer algae or detritus. Leaf litter would be good for them. Can be caught in most nets unless very young, and they'll survive until eaten, providing stimulation and exercise for the fish.
Just fyi, blackworms often have a few leeches with them. I find that most of them are already dead. Those I toss [ they're white, as are dead worms ] but live ones are taken by the Bettas just as eagerly as the worms are. They hang onto the end of the chopstick quite tightly. They used to gross me out, but not any more, though their big cousins sure would.
The leeches are harmless, so if one escapes being eaten for awhile, won't hurt anything. Not big, stretched out they might be an inch long, contracted they're no more than 1/8" diameter bumps, a dull greyish-brown colour. The few escapees I've had seem to prefer living on the underside of frogbit leaves and if I find one there, I push it onto a chopstick with my finger and give it to a Betta.
Blackworms can survive for weeks in a tank, and if there are enough of them, potentially can become permanent or semi permanent residents. Usually they reproduce by fragmentation, sexual reproduction being very rare in a tank setting. If you have bottom feeders like loaches or cories, don't feed them for a few days and extra worms will soon vanish. Even Bettas will hunt them on the bottom.