As stated, it will vary from provider to provider.
In my opinion, work related to ensuring advertised services and features work should carry no charges.
Most solid providers adhere to that opinion.
Furthermore, the charge by providers can vary from less than the original poster stated to a lot more.
Lastly, in terms of our company, we use the 15-minute rule for existing clients (as it relates to hosting, not managed services). If it takes 15-minutes or less (and the client is not taking advantage of it), no charge.