After Pentecost, Peter & the apostles first baptized 3,000 people (in Jerusalem) and their work began. However, I am not sure exactly when they dispersed and started evangelizing outside the city. They may have started in Jerusalem and stayed there for a bit.
(Luke 24:49) “I am going to send you what my Father has promised; but stay in the city until you have been clothed with power from on high."
Acts 1:8 “But ye shall receive power, after that the Holy Ghost is come upon you: and ye shall be witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost part of the earth.”
(Jesus says to wait until they received the Holy Spirit at Pentecost.)
The next information we get is about Philip baptizing the Ethiopian treasurer and Peter receiving the vision to go to Cornelius’s house, so they may have stayed in Jerusalem for a bit until the Spirit urged them to travel, not sure about the timeframe.
