One playthrough is around 3 hours. There are 4 endings and a side story. It probably takes around 5-7 hours to complete the whole game. (estimation depending on reading speed)
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I'm a bit confused by the question. Are you asking about how to make the game, or are you asking for a walkthrough?
If it's the former, I used a software called Flash MX. It's not particularly user-friendly. I would recommend you Ren'py instead.
If it's the latter, the walkthrough of the game is available on my site: http://zeiva.net/otome/x_note_guide.html
Technically the game is a browser game made with Flash. As long as your Linux can play Flash, then the game is playable. As for the demo, I will update it with the browser version, so you can give it a try. Hope it works out for you.