Here is a simple formula to estimate when PAX will complete. This is useful for planning when to be online.
PAX delivery P(t) increases over time t from 0 to a final number P(T) which is determined by city level.
Measure P at one point in time P(1) and a second point in time P(2). If the time interval between recordings is EXACTLY 1 hour, then P(2) - P(1) is the hourly rate of PAX delivery.
The time to completion in hours is then calculated as [P(T) - P(2)] / [P(2) - P(1)].
This estimate is only as accurate as the consistency of the rate of PAX delivery. If people change the trains, then the delivery rate changes and the result would have to be re-estimated.