Sleeping Dogs

Actually, you can't do it whenever you like. You don't have the ability to hijack the trucks until...well...after the mission where you hijack the truck...and already gotten the achievement.

I don't know if you can do truly this "whenever you like", or if certain criteria have to be met beforehand, but you absolutely can do this before you do the mission where you hijack the truck (Payback).
I haven't done any mission where I hijack any truck yet. I haven't had any hijacking tutorial during the handful of missions I have done so far. I just finished the Amanda mission a little bit ago, and, immediately after that, got the achievement getting away from the cops in the Chicken Van after Popstar shoots the dude during the 3rd part of the first Case for Teng. I accidentally hijacked one of the police cars (definitely wasn't a truck of any kind) that was chasing me after the shooting (still not sure how I did it), and the achievement popped at that point.
It's kind of funny, because I actually got too far away from the Chicken Van by the time I realized what had just happened, and actually failed the mission before I could get back into the van and had to restart from the previous checkpoint. But, it is definitely possible to hijack before the Payback mission with the hijacking tutorial.