... and that's why TTs only go back in increments of one hour :D

More seriously, 'tis magic. It works how the person who made it expected it to work, if Harry is correct, whether that's Aristotelian acceleration or just our intuitions about how "moving backwards in time" should look.

(Maybe it simulates a "marker" sitting in your position as the timeline is rewound. What happens if you travel to somewhere a wall was just built?)