These are exactly the symptoms I'm experienceing with two Dell notebooks and Windows 8.1 with 12.1.4 MP1a of SEP. I have a case open right now and we are not to resolution but I've isolated this a little further.
1. The 600 seconds are the default timeout for gpo script failures in a Microsoft active directory environment
2. We are running SBS 2008 and there is a default GPO called "Windows SBS CSE Policy" attached to the domain.
3. With the above GPO disabled, the log messages and slow boot before the login prompt dissappear.
4. This GPO runs a startup script(before login) which loads clientagent.vbs which is responsible for installing the windows small business server client agent"
5. I have a support case open and I've forwarded this information and I'm waiting for a reply as to what action to take(case 06555017)
6. This GPO is dual purpose for scripting(clientagent.vbs) the installation of the 32 bit and 64 bit versions of the client agent.
I really don't think we require the "Windows Small Business Server client agent" any longer but you never know. It is used for software delivery to client computers in the SBS environment. Can anyone also experiencing the 600 second delay confirm that they are operating in an SBS environment?
Thanks,
Matt