as many times as they want. Hello i'm bettalu(Luis) the breeder here, and bettas can breed as many times as they are intrested in.
I had bettas breed once(female) and never had the intrest in breeding again.
Males on the other hand can breed right away after they are removed after the fry hatching(after 3days of hatching).
Females on the other hand, have to wait 3 weeks after spawning to produce enough eggs to engage in the spawning act again. Anything earlier is aggravating for the female and will be hostile and aggressive to the intrested male.
For further info and questions on breeding please as me and i'll be happy to help you to all my experiance and knowledge as possible!

Hope to hear from ya soon! and welcome to our betta family, stay with us for a while

and you'll learn and meet great people with the same passion for bettas as U!