Thanks for playing.
You're right. The timer function isn't very clear. It only resets when you go back to the pizzeria and it's probably way too quick.
(The idea behind the timer was: You pick up a bunch of pizzas at the pizzeria and each of those customers expect their pizza within 30 minutes (60s). They don't care how many pizzas you've delivered along the way. Unfortunately that wasn't made clear to the player in any way.)