In my experience, support response time is directly proportional to the severity of the issue.
Any non-critical enquiries I make are generally answered within 24 hours or so, but if the issue is critical (site outage etc.), the response is much quicker, usually only an hour or so, depending on the time of day and the number of pending support requests.
Although, I must admit, my experience is limited, as I have not had to make too many support requests. Generally (to borrow a phrase from Apple) 'things just work'.
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