Mario clock is a 2009 game that was released for the Nintendo DSi, It's just a clock, but there is a game where you have to reach to 12 to beat the game, Is it possible to speedrun?

Generally speaking, if it's a game, and it has some sort of win/end condition (or at the very least, you can define an arbitrary end point for a run), then yeah you can technically speedrun it.

That said, Mario Clock is a two-button autoscroller with no optimization potential, that revolves entirely around coin grinding, so I can't imagine that it's interesting, or fun, or challenging, etc.

Actually, in June 2020, I completed a Mario Clock Speedrun with a time of 4:30. I found out that time by using the clock built into the game.