The leap day was introduced as part of the Julian reform. The day following the Terminalia (February 23) was doubled, forming the 'bis sextum - literally 'double sixth', since February 24 was 'the sixth day before the Kalends of March' using Roman inclusive counting (March 1 was the 'first day'). Although exceptions exist, the first day of the bis sextum (February 24) was usually regarded as the intercalated or 'bissextile' day since the third century. February 29 came to be regarded as the leap day when the Roman system of numbering days was replaced by sequential numbering in the late Middle Ages.

Gb8-22 and Gb8-23 were identical, bis sextum, and Gb8-27 was at the 1st day before the Kalends of March. There were 2 (bis) days needed for the Pleiades.

... Väinämöinen set about building a boat, but when it came to the prow and the stern, he found he needed three words in his rune that he did not know, however he sought for them. In vain he looked on the heads of the swallows, on the necks of the swans, on the backs of the geese, under the tongues of the reindeer. He found a number of words, but not those he needed. Then he thought of seeking them in the realm of Death, Tuonela, but in vain. He escaped back to the world of the living only thanks to his potent magic. He was still missing his three runes. He was then told by a shepherd to search in the mouth of Antero Vipunen, the giant ogre. The road, he was told, went over swords and sharpened axes. Ilmarinen made shoes, shirt and gloves of iron for him, but warned him that he would find the great Vipunen dead. Nevertheless, the hero went. The giant lay underground, and trees grew over his head. Väinämöinen found his way to the giant's mouth, and planted his iron staff in it. The giant awoke and suddenly opened his huge mouth. Väinämöinen slipped into it and was swallowed. As soon as he reached the enormous stomach, he thought of getting out. He built himself a raft [cfr The Heavenly Raft, θ Aquilae, *305], and floated on it up and down inside the giant. 

The giant felt tickled and told him in many and no uncertain words where he might go, but he did not yield any runes. Then Väinämöinen built a smithy and began to hammer his iron on an anvil, torturing the entrails of Vipunen, who howled out magic songs to curse him away. But Väinämöinen said, thank you, he was very comfortable and would not go unless he got the secret words. Then Vipunen at last unlocked the treasure of his powerful runes. Many days and nights he sang, and the sun and the moon and the waves of the sea and the waterfalls stood still to hear him. Väinämöinen treasured them all and finally agreed to come out. Vipunen opened his great jaws, and the hero issued forth to go and build his boat at last ...