Ever the logical one, although I'm not sure if his other videos are of use, they're all for speedstacking, and the only one I watched looked extremely conspicuous as well.
The lights behind him look the same, the clock looks fine to me, and you can hear the sound of a train passing by which sounds realistic. It also wouldn't matter if he didn't time it with the stackmat because his time is actually 28 seconds. He starts at 0:06 and ends at 0:34.
Perhaps the frame skipping really isn't frame skipping. Perhaps in the middle, he did a stop-motion animation to make the clock and stackmat look realistic!