How soon can I get my I-485 approved after receiving my EAD?

You can check Case Processing Times at USCIS based on the closest Field office to your residence:
https://egov.uscis.gov/processing-times/

Processing times fluctuate based on workload and resource limitations of the California Service Center. I-485 processing is significantly backlogged at the present time, but usually an I-485 should not take longer than 3-4 months to process. It is likely that the CSC will allocate additional resources to reduce the I-485 backlog, or they may transfer these applications to another service center to catch up with their processing time goals.

You should anticipate notice on your I-485 shortly.

It depends on cases. The average processing time for I-485 is under 1 year.

Both processes should take about the same time. It is likely that your I-485 application should be approved soon, unless there are issues with the application that are being investigated.

Processing times will vary from service center to service center, from form to form, and for each U.S. consulate. Furthermore, processing times vary and can change without notice! Current processing times, according to USCIS, for I-485 applications at the California Service Center are four months, but, again, that is only an estimate. It still may be helpful to make an inquiry to the National Customer Service Center (be nice in your inquiry!).

USCIS is posting about six months for I-485 to be processed. The consulate processing also will take a similar time period, as it takes about two months for USCIS to send the file to National Visa Center (NVC) and another month for NVC to issue a fee bill so that an applicant will be able to pay the visa fee bill and start the DS-260 with civil documents process, and another three to four months for the Consulate office to issue an interview appointment, sometimes longer depending on the consulate post. Unless you suspect that your application had some flaws, I would advise patience.

It is not unusual for I-485 processing to take six months or longer, due to the large volumes of applications. Consulate processing can sometimes be quicker, but it depends on the consulate. Many of my clients from China are actually experiencing longer processing times at the U.S. Consulate in Guangzhou. Again, this is in large part due to the increase in numbers of petitions/applications. In contrast, consulate processing times in Hong Kong and other countries tends to be quicker.

The processing time is estimated to be four months. However, it appears you''re currently five months out from filing. It''s a good sign that you received your employment authorization document. Hopefully, you should hear word on your I-485 shortly.