most sealed ball brgs such as used in motors and alternators
have a 5k hour lifespan, some a bit more and it depends on various factors
heat, humidity, dirt, loading, shock loading, etc.
i would plan on having spares and changing them annually in any machine that turns
1800rpm or more, maybe a longer at reduced speeds.
probably longer at reduced speeds
my opinion based on what i have read somewhere in a brg book long ago while working
as a millwright.
now if you have tapered rollers and an oil bath, they can run for a very long time
at lower rpms such as those in a windturbine.
bob g