Our Crawl Timeout feature, which can be found in test settings allows you to set a limit (in seconds) for the time it takes to receive the first byte of data(TTFB). If we do not receive the first byte in the specified time then you will receive an alert through your configured contact group.
This feature cannot be used to alert on slow “performance times”, as it only measures to the first byte which is defined as “the duration from the virtual user making an HTTP request to the first byte of the page being received by the browser.” Although it could be said that there is a correlation between performance time and time to first byte which can give you a rough idea of how one stat is operating by studying the other.
Thus, using the Crawl Timeout feature will enable you to identify occasions where your server is not able to handle requests as fast as is needed. Remember to set it at a number than is reasonable for the content you are monitoring, dynamic content will usually require more time.