He needed to hear the gospel (the good news) first.
In Acts 2, Peter preached the Bad News - you are sinners and are going to hell.
The people were cut to the heart "Brothers, what shall we do!!??" Notice that they well and truly believed at this point. They were desperate for an answer to this issue of sin.
Peter then told them the good news - how to have their sins forgiven! "Repent and be baptised for the forgiveness of your sins".
(It doesn't get clearer than that - does you bible say something else? Do you have a translation that reads "Repent and be baptised because your sins have been forgiven")?
Note the urgency! You get baptised as soon as you find out the truth after you have come to faith and believed the good news.
With the jailer "immediately he and all his household were baptized." Acts 16:33.
The Ethiopian immediately after hearing the good news See, here is water! What hinders me from being baptized!?
As stated before, the longest time between believing and being baptised was three days - and Paul had some serious repenting to do!
So what if someone wants to get baptized 3 months later for personal reasons?
There are plenty of verses that do not mention baptism..
Acts 5:14 And more than ever believers were added to the Lord, multitudes of both men and women,
Acts 11:21 And the hand of the Lord was with them, and a great number who believed turned to the Lord.
Acts 11:24 for he was a good man, full of the Holy Spirit and of faith. And a great many people were added to the Lord.
Acts 13:12 Then the proconsul believed, when he saw what had occurred, for he was astonished at the teaching of the Lord.
Acts
13:48 And when the Gentiles heard this, they began rejoicing and glorifying the word of the Lord, and as many as were appointed to eternal life believed.
Acts 14:1 Now at Iconium they entered together into the Jewish synagogue and spoke in such a way that a great number of both Jews and Greeks believed.
They went back, and still no water baptism..
14:22 strengthening the souls of the disciples, encouraging them to continue in the faith, and saying that through many tribulations we must enter the kingdom of God.
Acts 16:5 So the churches were strengthened in the faith, and they increased in numbers daily.
Acts 17:4 And some of them were persuaded and joined Paul and Silas, as did a great many of the devout Greeks and not a few of the leading women.
Acts 17:12 Many of them therefore believed, with not a few Greek women of high standing as well as men
Acts 17:34 But some men joined him and believed, among whom also were Dionysius the Areopagite and a woman named Damaris and others with them.
Acts 19:18 Also many of those who were now believers came, confessing and divulging their practices.