Jaiminīya (Talavakāra) Brāhmaṇa 2-8.307.p4

2-8.307.p4

tadyatsaptamasyāhnaścaturviṃśaṃ bahiṣpavamānaṃ bhavati caturviṃśatyardhamāsassaṃvatsaraḥ

As to why the Bahiṣpavamāna of the seventh day is twenty-fourfold: twenty-four half-months are the year;