It is required for the validity of performing it to have the intention established from the night, or an intention concurrent with the dawn; this is because these fasts are not specified, so the intention must be established until they become specified, as mentioned in the explanation of Al-Wiqayah p. 234, and 'Umdat Al-Ri'ayah 1: 307. If someone fasts with the intention after the dawn has risen, it will be considered a voluntary fast, and he must make up this voluntary fast if he breaks it.