Some googling yielded:The flower, which opens in the morning around 8 a.m., has eight yellow nectaries alternating with the eight filaments at the base of the ovary, bound together by a cushionlike swelling (Knuth 1909*, pp. 341 - 342). The flower (fig. 56) secretes nectar in copious amounts, but only in the morning hours, during which time it is highly attractive to bees (Phillips and Demuth 1922). Toward noon, the flow lessens, and during the afternoon honey bees usually abandon the plants. Pollen is also collected by honey bees from buckwheat.https://www.apiservices.biz/htm/pollination_handbook/buckwheat00000000037A9644.htmlWhich tends to confirm what others have commented on.