When you reach a pickup or a delivery, tap Arrived at the pickup (or Arrived at the delivery). The job then shows "Arrived" with the time. Your company may charge the customer waiting time from that tap until you tap Picked up or complete the delivery, after some free minutes, so tap it as soon as you get there.
It works with no signal too: the tap is saved on the phone and sent with its real time. Older versions of the app do not have the button; then no waiting time is worked out, and the office can add it on the job instead.