I think your question is completely dependent on the state of the network. I know when I first got my network up and running there were always small little things that became issues that needed to be addressed. That first week I probably spent 20-30 hours installing and getting things worked out. Now probably an hour a week unless something changes (windows update breaking MSE, Updox connector service not working correctly, Quest lab interface not syncing, etc).
The key is to get things to the point that you never go to your IT closet - ever. IT departments should not be seen or heard from (reference a BBC program on netflix - The IT Crowd).
I have a tendency to 'try something new' which seems to occasionally disrupt things for a couple days as I try to fix things but I'm hoping moving things to VMs will help alleviate the effects of my tinkering to some extent!
On average I probably spend 1-5 hours a week with helping people with their desktop issues but the servers pretty much just run in the background (I have 2 servers (SBS 2011 and a terminal server), 10 computers, 10 terminals and a few laptops and smart phones - 4 providers (2 fresh out of residency this past July), 12k patient files, and 8-10 employees)
