R’ Gamlial said to R’ Yehoshua, ‘I command you to come before me with your stick and your money on the day that in your calculations would be Yom Kippur’. R’ Akiva met R’ Yehushua and saw he was feeling bad. He told him that whatever R’ Gamlial sets as the month must be accepted so if they see the moon or not, the Bais Din Hagadol establishes the month.

R’ Yehoshua came to R’ Dosa ben Hurkinos and was told that as we must follow the Bais Din of R’ Gamlial the same is with all battai dinim since Moshe Rabeinu.

R’ Yehoshua took his stick and his money and came to R’ Gamlial in Yavneh on the day he thought was Yom Kipper.

R’ Gamlial stood up and kissed R’ Yehoshua on his head and said to him ‘come in peace my rebbe and student’. My rebbe in wisdom and my student who accepted my words.

Rosh Hashana 3:1

If Bais Din accepted the witnesses but did not have time to say ‘mekudash’ and it night time fell, Bais Din must make Rosh Chodesh the next day.

If a large Bais Din saw the new moon at night, the next morning 2 of the bais Din say before three that they saw the new moon.

If a Bais Din of three saw the new moon at night, the next morning 2 of them should become witnesses and have the third judge and two more people form a new Bais Din to accept the 2 witnesses.