168057 2017-02-09 10:46:31 -0800 [Navigation Timing] navigationStart and DOM timings in Unix epoch, other timings 0-based for Back-Forward navigations 2017-02-16 22:33:56 -0800 1 1 1 Unclassified WebKit Platform Safari 10 iPhone / iPad iOS 10 NEW P2 Normal --- 1 nic joepeck cdumez joepeck simon.fraser oldest_to_newest 1274917 0 nic 2017-02-09 10:46:31 -0800 Hi, We're seeing many cases where on Back-Forward navigations, the NavigationTiming timestamps are incorrect. It appears that navigationStart is Unix-epoch based, along with the dom* events. However, all other timestamps are 0-based. It also appears navigationStart happens after the dom* events. Example 1: Mozilla/5.0 (iPhone; CPU iPhone OS 10_2 like Mac OS X) AppleWebKit/602.3.12 (KHTML, like Gecko) Version/10.0 Mobile/14C92 Safari/602.1 navigation.type 2 // back-forward redirectStart 0 redirectEnd 0 navigationStart 1486655091185 fetchStart 0 domainLookupStart 2 domainLookupEnd 27 connectStart 27 connectEnd 50 requestStart 52 responseStart 434 responseEnd 0 domLoading 1486655020306 domInteractive 1486655044330 domContentLoadedEventStart 1486655044330 domContentLoadedEventEnd 1486655044339 domComplete 1486655088205 loadEventStart 0 Example 2: Mozilla/5.0 (iPhone; CPU iPhone OS 10_2_1 like Mac OS X) AppleWebKit/602.4.6 (KHTML, like Gecko) Version/10.0 Mobile/14D27 Safari/602.1 navigation.type 2 // back-forward redirectStart 0 redirectEnd 0 navigationStart 1486648661894 fetchStart 0 domainLookupStart 0 domainLookupEnd 0 connectStart 0 connectEnd 0 requestStart 3 responseStart 259 responseEnd 0 domLoading 1486648620150 domInteractive 1486648620956 domContentLoadedEventStart 1486648621014 domContentLoadedEventEnd 1486648621070 domComplete 1486648652486 loadEventStart 0 This doesn't happen all of the time, but in one data set, we're seeing it in 17 out of 254,357 beacons. It doesn't appear to be all Back-Forward Safari beacons, as there are 27,593 other Back-Foward beacons in that dataset whose timestamps look OK. 1275073 1 joepeck 2017-02-09 15:24:06 -0800 I can look at this.