Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Canons of the Councils of Ancyra, Gangra, Neocæsarea, Antioch and Laodicea, which Canons were Accepted and Received by the Ecumenical Synods.: Canon XLV

Canon XLV.

[Candidates] for baptism are not to be received after the second week in Lent.

Notes.

Ancient Epitome of Canon XLV.

After two weeks of Lent no one must be admitted for illumination, for all such should fast from its beginning.

Van Espen.

To the understanding of this canon it must be remembered that such of the Gentiles as desired to become Catholics and to be baptized, at first were privately instructed by the catechists.  After this, having acquired some knowledge of the Christian religion, they were admitted to the public instructions given by the bishop in church; and were therefore called Audientes and for the first time properly-speaking Catechumens.  But when these catechumens had been kept in this rank a sufficient time and had been there tried, they were allowed to go up to the higher grade called Genuflectentes.

And when their exercises had been completed in this order they were brought by the catechists who had had the charge of them, to the bishop, that on the Holy Sabbath [Easter Even] they might receive baptism, and the catechumens gave their names at the same time, so that they might be set down for baptism at the coming Holy Sabbath.

Moreover we learn from St. Augustine (Serm. xiii., Ad Neophitos,) that the time for the giving in of the names was the beginning of Lent.

This council therefore in this canon decrees that such as do not hand in their names at the beginning of Lent, but after two weeks are past, shall not be admitted to baptism on the next Holy Sabbath.