Failed this method one year ago, I was found after like 12 hours I think since my last text message was around 7am and found at 7.30pm.
Spent 7 days in coma and am now deaf from one side and my leg on the same side not working correctly due to nerves damages.
I think my mistakes were to do it in my bedroom wich is too large for this (~15m2) and to tell a friend that I was commit suicide soon (without telling when), a few hours without news from me and she called my mother and rescue services.
So, if I can give you an advice from my personal experience, make absolutely CERTAIN that nobody will find you before at very least 12-24 hours to be sure since you will sure fall into coma but it can take time to fully ctb.
Hope you will succeed where I failed and find peace.