In temperate varieties of maize or sorghum, lateness conveys high yield potential. By contrast, late maturing tropical sorghum varieties (>150 days grain to grain) do not yield more grain than early ones maturing in 90 days. Variation in crop duration is needed in Africa to adapt to the duration of the rainy season that varies with location (Curtis, 1968). Studies in Mali (Clerget et al., 2008) indicated that phenology is the key to understand this phenomenon. This paper provides further evidence.