This can be achieved in Timed
mode, but i suggest Casual
as it counts the time up rather than down so you can tell how long you have left easily.
If you turn Auto pencil
on and set the show errors to Deluxe
(Found in Help + Options - Settings - Helpers
) will make this very easy but to help you more, you could use an online solver, here's one for 9x9
However if you'd like to 'cheat' a little bit instead of selecting any puzzle choose LE01
Here's the solution for it Jayour tells me that you can fill out all bar one square and exit (Without saving) and then load the autosave and the game's timer should of reset.
Here's a video of the puzzle being solved.