Hi, your boyfriend's predicament is in fact very common in which an applicant is led to believe that a job offer is forthcoming and is left to wait an excessive amount of time for an answer. You write that he received a conditional job offer and that he took the physical and background tests. Is the condition of the job offer based on these outcomes?
In answer to your question, there is no specific amount of time that it takes to hear back from a prospective employer when an offer is expected. I will tell you this though, the key factor in any hire is urgency. If an employer really wants to hire someone and needs this person urgently, then no matter the job- a concrete offer is typically extended almost immediately.
As I see it, your boyfriend has 2 options. Either be pro-active by contacting the hiring authority and respectfully requesting an update as to his candidacy or .......move on. My experience is that time kills all deals. My best advise would be for your boyfriend to move on. It's probably not what he wants to hear, but it is reality. Human capital is any company's most precious resource. Why would he want to work for an organization that takes too long to make decions? If he does in fact get the job and at some point needs support, how long will he have to wait?