In my opinion a good time to reach out in regards to your final interview is anywhere from 1 to 2 weeks. Completing final interviews with multiple candidates can take time when you factor in everyone’s schedules.
In any case, I would recommend that if you have not heard back from the company once two weeks have passed since your last interview, follow up with an e-mail. If 1-2 more weeks pass and you still have not heard anything, I would follow up with a phone call. In both of these communications, it is important for you to stress that you know how busy they are and that you are very excited about the opportunity.
I have always recommended that if a candidate is going to send 'thank you' emails they do it the same or next day following the formal interview. Send 'thank you' emails to everyone you interviewed with. Be brief (don’t send a thesis) reiterate your interest in the role and open the door to any follow up questions they may have.
Before you leave the interview, it's common for the recruiter to give you an idea of next steps - i.e. whether they are considering other applicants, how long the process could take, what extra materials they need from you.
Did the recruiter say when you should expect to hear back from them? If so, allow it to get to that date. If after a couple of days from that time you haven’t heard, then definitely reach out to them to see where they stand.
If you did not initially set up a time frame, wait one week and call.
There can be several reasons for a delay in the process so just want to be sure that you’re professional in your approach and mindful of things that can come up. This is also a good opportunity to reiterate your interest in the role as well as your key strengths that you would bring to the position.
It is important ... not to be overly aggressive in your follow-up. Respect the fact that the hiring managers are very busy and other priorities can take precedent over hiring decisions.
If you find that you are not selected for the position, be professional. You never know what opportunities could come up in the future where you may be considered!
If a week goes by and you still haven't heard from them after sending an e-mail, I think trying to phone them would be an appropriate next step.