The timer that calculates syncTime (qtdeclarative/src/quick/scenegraph/qsgthreadedrenderloop.cpp:1178) is in the wrong spot. It seems that if the scenegraph isn't updated, the thread sleeps until VSYNC, and this wait is added to the value of the timer. This means that on frames where the scenegraph isn't updated, the value reported is much too high. If I'm not mistaken, and this really is a bug, I'll gladly provide a patch.