It depends on a lot of factors. I've had bearings last well past 10,000 kms, and I've had some go bad with less than 1000 kms. In my experience, as an amateur mech, who does all my own work, only one time that I can specifically recall could I feel the BB being "bad" while riding. Every other time, it was diagnosed while cleaning the bike or changing a chain. The bearings felt rough when turning the crank, so I pulled the crank, and turned the bearing by hand to confirm. There is also a fair amount of evidence that Press Fit BBs (to include BB30, which is assembled by threading the two sides together) can develop ticks and clicks, because the pressed bearing cartridges are moving ever so slightly in the shell, but the bearings remain good. I do concur that you should eliminate the other items others have already mentioned, first, before going after the BB.