Not clear is it: I meant that I'm getting at least twelve months use before I have to change the bearings.
I honestly doubt I've had to do it even every two years: I change the bearings when buying second-hand as a matter of course, so it's hard to remember when I changed what and for what reason.
Obviously it depends on the use they get, but annually at the very minimum for me.
I can't really remember (it's so infrequent), so I'm erring on the side of caution.
If your bearings need changing every six months, then you're doing something wrong (or a lot of CX).