Probably just a plot hole. This did not happen in the book.

They fled after he dialed the code. He just didn't hit the call button right away - I assume to give the drivers time to run. More likely than not, once he entered the code it started some kind of clock or setting that the drivers could see. The fact they all got out and ran tells me there was some kind of alarm or clock or something that went off in all the trucks showing they were going to blow.

They fled before. That is what has been bugging me. Anyway it can be anything. Maybe they put some alarm that would go after they drive for some time.

Good question Maybe the weapons inside make some kind of sound warning of their detonation? They fled the vehicle before or after Pine dialed the code? I don't remember

It seems unlikely that they were hired by Pine. It is more likely that they were hired by the buyer. After all the trucks were to go the buyers place ultimately.

They were working for Pine. He had set the whole thing up ahead of time. Remember he went with his friend and some other guys the night before to plant the bombs. I'm not sure if those were the same guys driving the trucks or if they were hired by them.
It's been a while since i saw it, but i believe they drive off and then suddenly stop and run away. It was after they were far enough away that Pine sent the signal to blow up the trucks.
What i'm not sure of is if he sent the signal that triggered the bombs or if he just sent a text message to someone who had a remote detonator.
Fraaaank. FRANK! Get my jean bin. Susie wants my jeans.
No she doesnt.