But there is something strange I noticed. The little spinning thing on the browser that indicates activity does not start spinning until after this delay.
I once noticed that it waited until an animated sequence on an ad finished its cycle. During the period the animation was finishing, the spinning thing was not rotating.
It even happens in the early morning (after midnight), so it is probably not traffic-related. But I noticed that there is a delay of almost 10 minutes if it happens near 4 am. But that one is different, because the spinning thing is spinning during that 10 min delay.