From www.pcworld.com

How to change the time period for Windows prompts to restart after updates

Posted by Erik Larkin

My colleague Robert McMillian at the IDG news service came across this great tip for changing the frequency for that oh-so-aggravating popup that comes up every 10 minutes after you install an update.

A blog poster at wdevs.com, who in turn found it from Codeproject, lists these steps:

Start / Run / gpedit.msc / Local Computer Policy / Computer Configuration / Administrative Templates / Windows Components / Windows Update / Re-prompt for restart with scheduled installations

I'll supplement just a bit to add that you should choose "Enable" and then type in how many minutes you want to wait, as pictured here: