Unfortunately, this is a hardcoded setting to 1000ms at this time and is not something that can be dynamically set as you found.
You actually want the appserver/static/WebsiteStatusCellRenderer.js file. The section of code you are looking for is between lines 72 and 96. Adjust the else if statements to the times you are looking to have the 5 different percent values; 0, 25, 50, 75, 100. These percentages are used to drive two different aspects of the display.
The first is the shape of the stopwatch icon that is displayed and how full it is. This is on line 100 in WebsiteStatusCellRenderer.js. The stopwatch font is then set in appserver/static/status_overview.css in lines 166 to 176.
The second is the setting of the class of the table data (td.response_time.response-+percent) set on line 105 in WebsiteStatusCellRenderer.js. This td class is then used in appserver/static/status_overview.css in lines 115 to 143 to define the color of the cell.
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