How long will an I-526 approval take after RFE for my EB-5 petition?

Contact USCIS regarding the RFE; generally, USCIS responds within 60 days after RFE submission. I-526 and H-1B are unrelated.

Your H-1B should not be affected if you are otherwise eligible. No one will tell you what the chances of approval are without reviewing your I-526 petition, business plan, and RFE response. If the response was prepared adequately and satisfactorily, then your case should be approved. Your attorney should be able to initiate a status request.

I would feel free to follow up with USCIS on the status of the I-526 after this length of time - they indicate follow-up allowed after 60 days. The H-1B will not have an effect on the green card or vice versa as the H-1B is a dual intent classification.

Processing times for responses to requests for evidence average 60 days. Nonetheless, USCIS is not mandated to respond within a specific time.

An H-1B is completely different and is a job based application if you have a legitimate offer and a legitimate employer-employee relationship. An RFE can be answered in 3-6 months or as long as they want to take. Very few I-526 decisions appear to be coming out of the IPO, and only I-829s appear to be adjudicated although there are reports of a few approvals being issued on direct cases.

Sometimes the RFE itself gives a timeline (60 or 120 days or something). If it does, use that timeline. If not, even 120 days may be enough to make an inquiry.

There is no way to know.