I'm with others here. If you have seat reservations, it suggests that you have status or paid full fare in which case you probably saw what was best already and if anything major has changed and further seats not available to you are now, you would probably see that at the very beginning of when OLCI opens.

If, as you say, it is a busy enough flight that you couldn't get either seats together or even separate seats to the front before, chances are that there won't be many empty seats to play with. Sure, someone can cancel, change their flight, or miss their connection, but this could happen so late it would be unlikely to help. Conversely, maybe the flight is so busy that the cabin is full and some people will be upgraded or downgraded or IDB'ed anyway, in which case, if seat changes occur, they will be handled by BA anyway without ever looking available to passengers. So personally, I'd just check in, and when you arrive at the airport, by all means, go to the check in desk and ask if any seats together have become available, but just waiting will likely bring you little beyond unnecessary stress.