The total time from start to finish for an employer-sponsored Green card is based on the country of a birth specific queue. Most of the countries have immediate GC availability except China & India. India has the longest waiting time in terms of GC availability. What this means is that if you are an Indian and started the GC process in 2019, you can't file an i485 application unless your country's Priority date reaches 2019. Hence, the total time apart from the timings mentioned above (for 3 mandatory paperwork) is this waiting time for your country's queue to reach your year.