Adjustment of Status - I-485

My wife and I had our green card interview 3 weeks ago in Harlingen, TX, after almost 9 months of waiting for the interview. We did not receive RFE or anything like that. Everything went well during our interview and we had more than enough evidence. The IO did not ask for any evidence. Our interview was straightforward and took only a few minutes. At the end of the interview, the IO told us that we were well prepared but the IO needed more time to review our files and that they dont not need any further information or documents from us. The IO also said we will receive a notice in the mail. One day after interview the online status for both Forms I-485 and I-130 changed to "Interview Was Completed And My Case Must Be Reviewed". It has been almost 3 weeks and we have not received anything in the mail. The online status has not changed either. Can anyone help me understand, how long do we have to wait for an answer? and how long is too long for an answer? Thank you very much.