Considering that it's the only way to spend fuel in the game except for a few minor exceptions (grenades being one of them) the timing really only depends on your fuel control rather than your decision making. Fuel control however solely depends on your map control because fuel caches are irrelevant in the current meta game. And apart from fuel caches there's no way to influence how much fuel control your mapcontrol grants you because the amount of ressources you get from each point doesnt vary as it did in coh1. So all teching does right now is giving a player with good mapcontrol an advantage which is something the call in meta didn't really change. Map control gave you a lead just like it currently does, maybe not to the same extent but it was certainly a major gameplay factor.
-> teching is pretty much superfluous
Except teching is not linear. (Except for poor Neo-Soviets, but even then there's still the matter of whether you invest in a heavy t3 or tech t4 quickly or use call ins)
What tech structures you choose to invest in is very important. Where you put your fuel is very important. An American who gets grenades and an ambulance before lieutenant or captain will have a very different 7 minute force composition, but a stronger early game.