How exactly are you attempting to add the Windows Time Service to the Platform within HQ? Are you creating a new Platform Service of the type Windows Service, or are you trying to monitor it as a process? The former would likely work best if that is not what you are trying to do. Visit the resource page for the Windows platform, and select New Platform Service from the Tools Menu. Provide a name for the service, then select Windows Service from the Service Type drop-down.
The "Access is denied" message could also mean the user context with which you are running the agent does not have permissions to query that process. By default, the HQ agent installs the service using the SYSTEM account, and runs in that user context. If you have changed this, you may have to take a closer look at system permissions to insure the agent can access that which is necessary to monitor the box as you would desire.
On the Availability checks and Alerting, the smallest collection interval for metrics is 1 minute in HQ. For all but real-time service delivery environments, this is thought to be adequate with just about every monitoring tool I've ever used. I'd be interested in hearing more about your environment and your specific needs as a point of information if this is not true for you.
