Here is a breakdown of the processing times associated with each step of the H-1B to green card process:
A. The PERM Labor Certification can take anywhere from six months without an audit to over eighteen months with an audit.
B. Having your I-140 approved depends on how soon your priority date will be current. If that will not happen for several years, the USCIS may push your petition back to be processed closer to your priority date.
C. Waiting for your priority date to become current with the posted DOS final action dates can be the longest waiting period for some applicants. Take a look at the most recent visa bulletin to see where your priority date falls. This wait time heavily depends on which country you come from. For example, as of March 2017, EB-2 applicants from the Philippines have no wait time while EB-2 applicants from India must wait over nine years. For H1B Visa Process Visit here
D. The processing time for your I-485 depends on which service center it has been sent to. Some service centers are busier and have a backlog while others may have a very short waiting period. You can refer to this database to see the current wait times.
At the end of the day, the processing times vary wildly. An EB-2 applicant from Mexico whose employer does not encounter a PERM audit may be able to transition from H-1B to green card status in as little as 10 months. However, an Indian EB-3 applicant will most likely find themselves waiting over a decade for their green card to process.
In order to get a better grasp of what the waiting times will be in your particular situation, be sure to consult with your immigration attorney.