24-72 hours is common from my experience, but that likely varies widely and depends on volume and resources.
If you're running this in the cloud and properly automated everything, and its not a billing issue, responding and fixing things could be as simple as a few hours.
If you're running your own physical machine, repair times for hardware issues can be days.
If you're on vacation for a week or longer, and are making a concerted effort to step away from technology and lines of communication, or worse hit by a small bus and in the hospital for any length of time, you may not be aware of issues for some time.
