Shatapatha Brahmana 13.2.1.7

13.2.1.7

tadāhuḥ yadubhe divā vā naktaṃ vā juhuyādahorātre mohayedvyuṣṭyai svāhetyanudita āditye juhoti svargāya svāhetyudite'horātrayoravyatimohāya

As to this they say, 'Were he to offer both either by day or by night, he would confound day and night with one another.' With 'To the Dawn hail!' he offers before the sun has risen, and with 'To Heaven hail' when it has risen, to avoid confusion between day and night.