Actually, I agree with Howard.
If bearings are packed and adjusted correctly, they will last many, many years.
I used to repack mine annually. I finally realized there was no reason for it. Cars had the exact same type of bearings and went many tens of thousands of miles between repacking. They yearly thing is corporate CYA stuff.
So with our last TT I let it go for a number of years and 40~50K miles before repacking them again. (During that time I would check bearing adjustment and brake condition yearly)
When I finally took them apart they were still perfectly fine and didn't really need any service at all.