Metrics Query the response time of URL

Hi guys, I’m new to Grafana and I want to make an alert through Slack.
I want to alert through Slack when the loading time of URL has over 1 second
My environment:

  • Grafana v4.4.2 (commit: 6d9cbdd)
  • worldping plugin 1.2.4

My metrics:
A: [worldping] [url] [frankfurt - probe] [https] [total]

-Panel Data Source: raintank

My alert config:

My graph

Slack throw an alert [No Data] but I only want alert will be thrown when the loading time of URL over 1 second.

How can I do? Any suggests.
Thank you so much