Of the compounds hemanta-śiśirau and ahorātre , the gender is like that of the first word, in the chandas ,
हेमन्तशिशिरावृतूनां प्रीणामि, अहोरात्रे इदं ब्रूमः ॥
This aphorism debars the general rule given in 2.4.26.
This applies to these words in all cases and numbers, not being confined to them in the dual number, though exhibited in the sutra in the dual number, as :- पूर्वपक्षाश्चितयः, अपरपक्षाः पुरीषम्, अहोरात्राणीष्टकाः 'The white fortnight is fuel-wood, the black fortnight is the dung-cake, and days and nights are bricks (of the altar of sacrifice).'
Why do we say 'in the Vedas'? Observe दुःखे हेमन्तशिशिरे, अहोरात्राविमौ पुण्यौ. In the Vedas the ordinary rules of gender are often set aside; this an individual example of the universally exceptional nature of the Vedic language.,