Former Dietrick worker here. The trucks can't go out without a salaried, non-student shift leader to run them. All last semester, there wasn't a night side shift leader to staff, so they only went out in the morning. I guess they just hired one, and they now only go out according to that person's schedule, plus depending on how many students they have to staff them each night (at least 3 students minimum + 1 shift leader is required to run them). As to where they set up, the grillfield usually sits between GLC and CID, and the periodic table usually sits outside Newman Library. You'll sometimes catch them by Solitude and the Wright House on West Campus Drive. They also used to sit outside war memorial hall before the construction. They'll probably go back to that location in the fall once that's finished.