How can I monitor CPU usage and processes on Windows Server 2012 as a service over a 24 hour period?

Windows Server has a built-in tool to show performance data in real time or to collect data in logs for later review. I think that this will do exactly what you are looking for.

See this article for a basic tutorial on using Performance Monitor for logging on Windows Server 2012 R2.

See this excellent article on all the tools available to you for examining performance on Windows (mostly interactive tools).