DB Engine :: System Failure Error Check Policy - Filter By Time Generated?

I have been searching for a means to change the System Failure Error Check policy that comes as part of the Best Practice policies. I want to look back 24 hours. The WQL query shipped with the policy doesn't have a WHERE clause component that looks at TimeGenerated. That query looks like:

IsNull(ExecuteWql('Numeric', 'rootCIMV2', 'select EventCode from Win32_NTLogEvent where EventCode=6008 and Logfile="System"'), 0)

After searching for an example of how to do this and not finding any that are specific to PBM, I decided to fall back to a very basic approach - use wbemtest.exe to try out where clause additions and see how they work, then plug the result into the policy and see if it works. As a start, I tried the following query using wbemtest.exe:

select Event Code
from Win32_NTLogEvent
where EventCode = 6008
and Logfile = 'System'
and TimeGenerated > '20130101010000.000000–000'

This works great in wbemtest.exe. My next step was to plug this into the policy condition expression as follows: IsNull(ExecuteWql ('Numeric', 'rootCIMV2', 'select EventCode from Win32_NTLogEvent where EventCode=6008 and Logfile="System" and TimeGenerated > "20130101010000.000000–000"'), 0)

When I try to manually evaluate this policy in SSMS, I receive an "Invalid Query" error message.I assume that SWbemDateTime isn't available to use inside Policy Based Management policies. All the examples of how to handle the kind of dynamic date creation I have seen are for use in PowerShell, VBScript, or SSIS. I've played with using DateDiff, DateAdd, and GetDate inside the query string, with no success.

Why does the ExecuteWql above fail?Is it at all possible to dynamically generate a datetime (say, 24 hours ago) as part of the query string parameter of the ExecuteWql call?What might that look like?