On the day of Pentecost, after the tongues of fire happened, Peter gave a sermon to some non-believers in Acts 2:
37 Now when they heard this they were cut to the heart, and said to Peter and the rest of the apostles, “Brothers, what shall we do?” 38 And Peter said to them, “Repent and be baptized every one of you in the name of Jesus Christ for the forgiveness of your sins, and you will receive the gift of the Holy Spirit. … 41So those who received his word were baptized, and there were added that day about three thousand souls.
They repented and were baptized the same day.
One day, Philip the Evangelist met an Ethiopian eunuch, Acts 8:
30 Philip ran to him and heard him reading Isaiah the prophet and asked, “Do you understand what you are reading?
The eunuch was reading Isaiah 53.
34 the eunuch said to Philip, “About whom, I ask you, does the prophet say this, about himself or about someone else?” 35 Then Philip opened his mouth, and beginning with this Scripture he told him the good news about Jesus. 36 And as they were going along the road they came to some water, and the eunuch said, “See, here is water! What prevents me from being baptized?”
Nothing.
38 And he commanded the chariot to stop, and they both went down into the water, Philip and the eunuch, and he baptized him.
Philip baptized the eunuch on the day he met him.
On another day, Peter was preaching to the Cornelius' household, Acts 10:
44 While Peter was still saying these things, the Holy Spirit fell on all who heard the word. 45 And the believers from among the circumcised who had come with Peter were amazed because the gift of the Holy Spirit was poured out even on the Gentiles. 46 For they were hearing them speaking in tongues and extolling God. Then Peter declared, 47“Can anyone withhold water for baptizing these people, who have received the Holy Spirit just as we have?”
No one.
48 And he commanded them to be baptized in the name of Jesus Christ. Then they asked him to remain for some days.
They were baptized the same day they heard Peter preaching.
Another case happened to John's disciples in Acts 19:
3 [Paul] said, “Into what then were you baptized?” They said, “Into John’s baptism.” 4 And Paul said, “John baptized with the baptism of repentance, telling the people to believe in the one who was to come after him, that is, Jesus.”
There were 2 conditions: repent and believe in Jesus.
5 On hearing this, they were baptized inb the name of the Lord Jesus.
Baptism celebrates the burial of the old life and the raising of the new life. Romans 6:
4 We were therefore buried with him through baptism into death in order that, just as Christ was raised from the dead through the glory of the Father, we too may live a new life.
When should you get baptized?
Right away after you have repented and believed in Jesus.
See also
Is baptism necessary for salvation?.
