Hail can cause seeds inside pods to bruise. This bruising can also cause pods to shatter prematurely, although the shatter tendency depends on the extent of hail. If only a few bruises, shatter loss should be minimal. However, if bruising occurs on more than 25-30% of the pod, and the spots turn white or brown, shattering is likely to occur. When those pods will shatter is difficult to predict.
Swathing early may save some of these pods. And because seed behind these bruises are not likely to finish filling anyway, delayed swathing will have minimal benefit to these particular seeds.
The key phrase here is “these particular seeds.”
The decision to swath a hailed crop should be based on a whole-crop assessment. Read here for tips.