This should work for you. It works for me. You should've got an email at 6am stating the node was down. I did a test where I copied my node down alert and changed the alert time frame. So when I turned my node off, I received an email from my normal down node alert. Then when my test alert started, I got another email stating the node was down. The only difference is that now the node down alert says that the node went down at the start time of my test alert, not the actual time it really went down.
So you must have an issue elsewhere. What version of NPM are you using? What does your trigger look like? Does the alerting work fine during 6am-6pm? Maybe the node that went down, may not normally trigger this alert?
