This is a question that lacks a definitive answer. Various steps are leading to your Green Card approval, and each of these steps requires varying wait times. However, if you are inside the U.S. as a lawful nonimmigrant seeking a change of status, here is a breakdown for the approximate wait time for every phase:
The PERM Labor Certification process usually takes approximately 8 months
Processing Form I-140 takes 6 months on average. However, you can use USCIS’s premium processing service which will shorten the processing time to 15 calendar days.
Wait time for your priority date to become current depends on your country of origin. It ranges from two months to 10 years.
Processing time of Form I-485, Application to Register Permanent Residence or Adjust Status, takes about 8 months. As is the case for Form I-140, USCIS’s premium processing service can be used for Form I-485 as well. This will shorten the wait time to 15 calendar days.
If you are outside the U.S. and using consular processing:
The first three steps above apply to you as well. However, after your priority date becomes current, you will need to complete the DS-260 online immigrant visa application and schedule an interview at the U.S. consulate or embassy in your country of origin. Therefore, the wait time until your immigrant visa is approved entirely depends on the U.S. Consulate or Embassy in your home country. However, you should not expect to wait more than a year.

Priority date is the date you filed your Form I-140. This date will then give you an educated guess as to when your priority date might become your current date.

Every month the Department of Labor (DOL) publishes a visa bulletin specifying the final action dates for waiting approvals, such as your Form I-140 petition. If the final action dates specified on the bulletin for I-140 petitions match your priority date, then your priority date becomes current. This means that you should wait for the result of your petition very soon!