If I drank a little bit of alcohol then took a sleeping pill shortly after, how long will I take me to die? Will I die?

No.  You'll wake up in your own vomit and have a splitting headache.

go seek help tf

If you wake up tomorrow dead, well, then there you go. 

Go and get a doctor’s referral to see a psychologist if you’re considering suicide.  It sounds like you’re severely depressed and that can be fixed with therapy and medication.  Lifeline is a good counselling service too, free and over the phone; as is Beyond Blue.  

You'll certainly die. It's impossible to say when though. You could live til 90 or be hit by a bus tomorrow.

Dunno, 60 - 80 years?  

I'm being flippant, but it's true.  Some booze + a sleeping tablet = no big deal.  Look, kid, this is NOTHING short of committing murder that will really seem all that important to you ten years from now no matter how bad you think it is.