is there a wait period from OPT to Greencard?

Generally speaking, the period of time between filing and adjustment of status interview at a local USCIS field office is approximately 6 months nationwide. If your boyfriend's OPT status exceeds six months past the date of filing, he will likely be okay working-wise as long as the case is approved on the date of interview. USCIS also offers employment authorization on the basis of a pending adjustment of status application to those who make application for it. Such employment authorization application on form I-765 is usually filed at the time of the rest of the I-485 adjustment of status application paperwork. That work permission normally comes within 90 days. Such document may prove especially beneficial if the case is not approved at interview since it then usually becomes difficult to know how long US CIS will take to adjudicate the case unless the immigration examiner is forthcoming with such information. Applying for employment permission at that time would take another approximate 90 days. I do note that in a marriage-based adjustment of status application case involving a US citizen petitioner, illegal employment is not a bar to approval. Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.  

If you are a US citizen, you can file a one-step adjustment application.  90 days later, your husband would get a work permit.  If his OPT expires before that, he'll experience another gap.