I am still on my original belts on my 25 yr old Hondas with well over 500 hours on each machine with very severe usage. Maybe Honda just used good belts, but normally you shouldnt have to replace belts every year, usually just when they show wear. They usually break when you are using the machine clearing snow, "Murphy's Law". Do inspect them every year or more often to try and avoid that from happening when in use.
When the belt adjustment has been used up and there is more than a half inch of deflection in tensioned run with the clutch engaged. With more slack in belt it will heat-up from slipping and then de-laminate.
Change your belts when they are cracked or stretched.Doing it when you have time is better than waiting til they break.If you wait,it’ll break right in the middle of use,usually during a storm.I keep extra set just in case.Dragging it back from 2 houses away is embarrassing.
i usually do it when they break but it is definitely a good idea to inspect for abnormal wear or damage and make sure you adjust the belts as needed. if you run out of adjustment and it still slips then it needs to be replaced but most machines are pretty good and have quite a bit of adjustment but some machines have way more adjustment than others.