From GameBrew - a wiki dedicated to Video Game Homebrew.
TimeHack is a DS homebrew puzzle game about hacking a timer, with additional options that enable you to edit the margin of error and hide the indicator to make the game more challenging.
The objective is to stop a timer and getting it as close as possible to the number requested within 3 attempts.
You can change the margin of error down to 0 to increase the difficulty of the game.
It also allows you to hide the counter, the indicator for the number of your attempts, as well as amount that you have missed or exceeded over the reached target.
Stylus - Full control
Up/Down - Change margin of error
A - Start/stop the counter
R - Hide attempts and numbers to reach target
L - Hide counter
Tested on DSTT/TTDS (firmware 1.17a12).