How long will you stay alive for after being bitten by a venemous rattlesnake?

i'm writing a book about a boy being bitten by a venemous rattlesnake whilst he ran away from home and whilst he's on the floor in pain days and days go by and he has an epiphany, the story has been inspired by 127 hours movie but its not an exact copy. so i want to ask if it will be able for my character to stay alive for long after being bitten, i mean i could easily make it that the doc tells him its a miracle or will that be just a bit. hmmm i don't know. please help