Laurence Stookey notes the development of the 40 days of Lent:

In the early centuries [of the church], forty days was the time sufficient for converts to make their final, intensive preparation for baptism; and thus a pattern for Lent developed.  (p79, Christ’s Time for the Church)

What is interesting to me is that many will take on the season of Lent–days of fasting etc–who would never recommend 40 days of preparation before baptism. In scripture, the pattern is repent, believe and get baptized, not repent for 40 days, then be baptized, or prepare to repent then get baptized. For Philip, if repentance and belief are apparent, it’s time to get some water. Separating an artificially imposed season of repentance is just as odd. If there is sin, repent of it now and believe. If sin is habitual and deeply ingrained, take a season to address it. But setting up a system that highlights (isolates?) mortification of sin for six weeks a year arose from an unhealthy understanding of baptismal preparation and seems to me to promote an unhealthy approach to sanctification.