Or just pay whetever's due when you return to exit. Having to schedule and reschedule sounds unnecessary to begin with.

You can only do that at a dedicated and fenced of garage or parking lot. You can't do that at the curb in the inner city. You have to pay upfront.

Without the app you have to find the meter, pay, print the receipt and get back to your car to put in in the window. Remember the time and get back.

With the app you can just start walking towards your destination while you start the metering.