If anyone is looking for something similar, this the modified version I've gone with - UTC for timing, ToLocal for display, with a server link to the node added in:
SELECT Server, '/Orion/NetPerfMon/NodeDetails.aspx?NetObject=N%3a' + ToString(NodeID) AS [_LinkFor_Server], MachineType,Last_Poll FROM ( SELECT c.NodeID, a.Caption as Server, a.MachineType, ToLocal(MAX(DateTime)) as Last_Poll , MinuteDIFF(MAX(DateTime), getutcdate()) as TimeSinceLastPoll FROM Orion.CPULoad c INNER JOIN ( SELECT NodeID, Caption, MachineType FROM Orion.Nodes where Status=1 and UnManaged=0 ) a ON c.NodeID=a.NodeID GROUP BY c.NodeID, a.Caption, a.MachineType ) as polling where TimeSinceLastPoll>30 ORDER BY Last_Poll