Trackmania

Head into the Simple Track Editor, place a start, place a finish right after it and validate it or save and test it. Every time you cross the finish line (as indicated by your time showing up on screen), press and then . This will allow you to immediately bring up the restart options and select "Improve". Considering that each run, including the initial countdown, takes only 4-5 seconds, you should have the achievement within 1-2 hours if starting from scratch. If you already have progress from the achievement for crossing 100 finish lines, it will take even less time.

Edit: Assuming you have the author time for your track, which should be 1.477 seconds, if you turn a little bit during each run, you’ll take a little longer than this. For some reason, if you press after seeing your time pop up in this case, you don’t have to go through the restart selection screen with the “Improve” option. This can make your runs even faster, at only 3-4 seconds, making this achievement unlockable within about an hour if starting from scratch.