What is the rule that says something in the lines of: if you don't verify your backups you don't have backups.
I feel that applies here, this doesn't need to take more than 10 seconds once a month (at least I would prefer it to be often enough that if it didn't come I'd recognize something was off - anything more than a month and I'd probably never notice if they stopped coming).
Each verification also serves the purpose of reminding you the service exists, that it is alive and at least gives you some indication and confidence that it will work when you want it to (also makes you think about it, after ten years maybe you'd want to update the content for it to still be relevant).
I feel that applies here, this doesn't need to take more than 10 seconds once a month (at least I would prefer it to be often enough that if it didn't come I'd recognize something was off - anything more than a month and I'd probably never notice if they stopped coming).
Each verification also serves the purpose of reminding you the service exists, that it is alive and at least gives you some indication and confidence that it will work when you want it to (also makes you think about it, after ten years maybe you'd want to update the content for it to still be relevant).