How long did it take St. Paul to travel from Antioch to Derbe on his first missionary journey?

AnswerRaymond E. Brown ('An Introduction to the New Testament') points out that in his undisputed letters Paul gives us no information about the first missionary journey, as if it neever happened. The itinerary has been called into doubt by some scholars, while others say there was no first missionary journey as described in Acts of the Apostles. It may be futile to hypothesise how long a journey may have taken, if we can not even be sure that it took place at all.