Dear Anonymous A,
Crossing my fingers for you that when you do hear back it will be with an offer! Try not to fixate on the 24-hour turnaround guarantee that is oft-feted with Final Round interviews. This turnaround time used to be true several years ago, but more and more, I hear about decision times taking longer to communicate.
In my case, it took McKinsey 6 days (if I correctly recall) to communicate my offer, L.E.K. Consulting a full week, and BCG just under 2 weeks. And most people I coach rarely get their offer in 24 hours. It's usually after the 48-hour mark has elapsed.
The good news for you (so far, anyway) is that clear Rejects do not require a lot of deliberation, so it's reasonable to assume you don't fall into this category. The only reason that calls for clear Rejects could be delayed is if the recruiter is the one assigned to handle Reject calls who has then elected to assign them to a certain day of the week to do them in batches.
The likely biggest reason for delays is the pipeline for Decision roundtables. At McKinsey, offers at the Final Round are usually assessed in decision roundtables. A group of colleagues receives the interview assessment notes from the partners and the roundtable (with the partner's participation, where possible) reviews and discusses the candidate's performance against the benchmark and votes the candidate in or out. I know from experience that individual decision cases can run for about 15 - 20 minutes. It therefore follows that if the decision committee in your destination office is only meeting for a few hours per day (or per week) and is working to schedule in the interviewing partners (which is often messy), then these committee processes could be delayed. Add to that an extended pipeline of other cases before yours which require 15-20-minute deliberations and you begin to see why delays can stake up. Finally, there is usually a co-ordination to ensure that your offer paperwork is delivered to you via e-mail as soon as possible after the offer call (usually done by the partner) takes place. If the recruiter is ready to hit Send but the partner is not ready to call, there will also be a delay.
This is how things worked at McKinsey when I was there. I am not certain how they work at Bain, so it is only a guess that there are some similarities. It's not easy to wait (no matter what anyone says), so I would recommend you just hang tight as best you can and try to distract yourself with other things you hopefully have going on. :-)