Passport renew waiting time

We reached the immigration office on 8.40am and got the number 1062, while the current number is 1022. With 40numbers in the gap. There are 2 counters working on this 10* number category.
After waiting for 1hour, the processed number is 1029. A rough estimation, it took 1hour to finish 7 numbers. To reached my number, it will take another 4.5hours.
If they procesed faster with 10numbers per hour, it will take 3hours to reach my turn.
Eventually, it reached my turn at 11.30am. It is 1 hour faster than estimated. :)
There could be few reasons of the faster process. 1-faster performance counter, 2-less trouble applicants, 3-some could have gave up to wait anymore.
During my turn at the counter, the whole process was less than 5mins. If that is happened to all, that would complete 12 in a hour and 2 counters would be 24. Nevertheless, the process could be intterupted by some reasons. 
That would be the simple way to count for my turn during the boring waiting time. for those in rush or short of time, recommended to come early and get your number quick :)