Your pair of bettas finished spawning and you have removed the female. Now what?
Make sure you leave a small light on near the aquarium if there isn’t one already. This will help the male to see the eggs. The male will not appear to do much for a day or two. He will hang out almost motionless under the nest and fan the eggs to circulate the water and keep fungus at bay. Assuming the eggs are not infertile or that dad doesn’t get the munchies, the eggs should hatch out in 36-48 hours depending on temperature. The fry will at first sink to the bottom of the aquarium and the male betta will madly try to catch them and pick them up and put them back in his bubble nest. Within 12 hours the fry will have absorbed enough yolk to be able to “glue” themselves to the glass or hang onto the bubbles vertically.
About two days after hatching the fry will be free swimming Free swimming means the fry are horizontal in the water rather than vertical with tails hanging down.
You can remove the male very carefully once all the babies are swimming horizontally. Note, there may be a couple who NEVER swim correctly and those will in time will die. If the great majority of the fry are swimming horizontally you can go ahead and take the male out. Your male betta is likely to have babies in his mouth so you have to try to catch him in between fry catching excursions. Make sure the water you place the male in is the same temperature as your breeding aquarium to avoid shocking him which can result in disease. I usually, very carefully, float a clear cup in the water that has a lip. The lip is important as it keeps the cup from banging into the side of the aquarium and squishing the fry. I will carefully catch the male with a small net or my hand (this takes practice) and then put him in the cup. If he spits out babies in the cup you can use a small eye dropper to gently and slowly suck them up to return them to the aquarium.
If you forget to float a cup and do not have an aquarium ready at the exact same temperature, you can use an eye dropper or syringe to carefully remove enough water into a cup or small jar and place the male in that. You can then float his cup in dechlorinated water and move him back to roomy accommodations after about an hour. Give him a few minutes to adjust to the larger home and then offer a betta pellet. If he eats it you can feed him normally. Caring for eggs and fry for a few days is horribly exhausting and your male may look very worn out, especially with very large spawns (spawns can range from 30 fry to 300 on up for very large females).
Next: what to feed the fry.