My test page contains a request for a script that will never return. The final outcome can be found in this Google Spreadsheet of Blackhole Request Timeout values. Here are median timeout values by OS:Android: ~60 secondsiOS: ~75 secondsMac OS: ~75 secondsWindows: ~20 secondsThe timeout values above are independent of browser. For example, on Mac OS the timeout value is ~75 seconds for Chrome, Firefox, Opera, and Safari. A general guideline is Frontend SPOF from a hung response ranges from 20 to 75 seconds depending on browser and OS.