Hi,
Once I had released Tandi from the Raiders and slain the gang for the loot, I left for the Hub to get a job at the Crimson Caravan.
Thus I traveled to Junktown this way. The departure are due on the 3rd and the 17th monthly and I wonder.re If I take the convoy to Junktown on the 3rd, can I go back to the Hub with the one on the 17th ?
Do I have to wait a certain hour at Junktown entrance or ask someone in the slum to summon the caravan ?
I would be greater than walking a week in the desert with my stubborn followers, yet it's not the lengthier walk on the map.
Thanks

If memory serves, you can take the convoy to get to Junktown but there are no convoys on the way back. I'm afraid you'll have to walk back (always save before leaving a town!)

I can't remember the exact schedule of the caravans in the original Fallout.
That being said:

A lot of F1 scripts were recycled into the sequel.
I'll tell you how caravan jobs are, in F2 (maybe it also applies to the original Fallout). You protect the cargo until you get to the destination, receive your payment, and the caravan driver leaves the town shortly after you arrived. He/she should be gone after 1 hour, even if the character has crippled both of his/her legs - I guess someone took it seriously after hearing "break a leg", at the beginning of a caravan run!

If you wish to travel back with the caravan, you must keep an eye on the watch (press "?" to check the time).