I've read most of WPM documentations but I can't find how the system checks whether a website is down and how long it lasts to change the status from critical to down after first Unresponsiveness and how much time it waits to change status from down to up (is there any polling and warning time?), I've already known how warning and critical alerts work (after a specific time that it is defined and can be managed after) but I can't find how it detects a website is down or up.