Alert - Node/Device Uptime Greater than 72 hours/3days

I am hoping that somebody can help me out with exactly how to configure an alert which will notify us via email when one of our windows servers uptime is greater than 72 hours/3days.

I am familiar with the alerting setup but I am thinking this has something to do with SQL queries and have tried 'WHERE Nodes.LastBoot < Getdate()-3' but then the trigger also asks for more criteria for example "Is greater than then a value" Do I fill this in too? Am i doing this right?

Any help would be much appreciated.