Happy to help, @andrew! Yes, the sentence has a clear future outlook. And in fact, there are two ways we can word it:
- We’re going to order food when he arrives (simple present) ~ Vamos pedir a comida quando ele chegar (simple future subjunctive)
- We’re going to order food when he has arrived (present perfect) ~ Vamos pedir a comida quando ele tiver chegado (compound future subjunctive)
The first option is the most usual.