During the entire spawning process. I'll feed them in the morning, then introduce them into the spawning tank in the afternoon/evening (with the female in the jar, separated from the male.) After 24 hours when the female is released, spawning usually occurs after 3-12 hours. The female is then removed after spawning and fed. The male stays in the tank and tends to the nest until the fry become freeswimming 3-4 days after hatching.
So, overall, the female will go approximately 2-3 days without food, and the male will go around 5-6 days. Every spawn is different. Bettas can go weeks without food and be fine, but this is why we condition them beforehand, so they can handle such an endeavor.