Having some users complain about the 90 minute warning they are getting after updates are applied to their workstations via System Center, stating that they'd rather it were longer. Leaving aside how absurd that is, does anyone know how to extend that warning out to, say, five or six hours? I can't seem to find anywhere in the Automatic Deployment Rule, Maintenance Window, or Update Groups to make that change.  Thanks in advance.

Try the client settings. I think that is what you are looking for.

Administration -> Client Settings -> Default Client Settings -> Computer Restart

• Edited by Kerwin MedinaMicrosoft employee Wednesday, August 26, 2015 1:43 AM
• Proposed as answer by Narcoticoo Wednesday, August 26, 2015 2:56 AM
• Marked as answer by Pete Schaub 14 hours 37 minutes ago

Thanks Kerwin, that's exactly what I was looking for.  Once I make a change to the Client Settings, do I need to re-deploy it to my collections to make it valid or is this automatic?

No need to re-deploy it.