Be less minutes than that I dare say. $20 an hour tech costs, then you have overheads and that's without a profit margin. I'd say 5 mins be more closer to the mark. Really gets down to how many support calls you have as if you have a couple admins who have to dip into a support queue, then their hourly rate would be higher. However if you have a nice frontline 1st line support pool with 2nd and 3rd for escalation model/scale then it will get cheaper.
That all said you have to factor in how much support they use and maybe your average user will need one or two tickets a year and then at the other end you the types who fail to read FAQ's and end up needing more support to use their computer, let alone the service and blur the lines contacting you for an issue that after some back and forth turns out to be the user's end. Those will be costly. So you balance things out - and go with the average and yet at the same time, dread some types of customers.
Hell, I am just a sysadmin/developer with minimum experience (2yrs) and make ~$32/hr.
In all fairness, support costs also include all of the techs' phones, computers, networking, software licenses for Teamviewer et al, and office overhead. So a $20/hr bill is pretty cheap for a minimum wage technician.