Oxycodone is metabolized pretty fast by the body - like 4 hour half-life (heroin has approx 8 hour half-life, methadone up to 90 hours), so my GUESS would be no longer than 3-7 days to kick the awful darkness of physical withdrawal (which is what it used to take me to kick junk). I kicked a 15 year methadone habit last year, and I don't think I could've managed it without ahem, 'medical marijuana' (shucks, I used the non-med mj too haha). I found eating it better, as it comes on slower and has more of a body stone - which you will most certainly appreciate. In addition to giving you relief from anxiety, and the sorta heebie-jeebies, I always found that weed just sorta lifted me outta that woeful "poor pathetic me" frame of mind....I'd suddenly find myself eating ice cream and grooving on music. I used Melatonin for sleeping - the sublingual ones - and took a couple per night. I usually avoided benzos ('usually' meaning...sometimes) but generally found that melatonin actually WORKS as long as you're lying in bed (on couch, whatever)with your eyes closed, and trying to go to sleep. Indicas worked better for sleep for me. DON'T stay in the house - go out if possible....go to your local pool and sit in that fuckin JACUZZI man, seriously. I used to like driving when I was in opiate withdrawal - or rather, sittin in the passenger seat (well, maybe not on the 3rd day, which I always found to be the peak) - and not drivin to like, Saskatchewan, but like simple driving errands....find a buddy who's got some errands to do (make BUDDY do the fuckin errands tho - you stay sweating in the car, haha) and just tag along - bag o' "medical" mj, couple litres o' gatorade, tunes - you're moving, scenery is changing, you're distracted, play some tunes (try to avoid Jane's Addiction and that Seattle stuff, lol). Go home, and watch some light-hearted bullshit summer movies - some Molly Ringwald 80s buffoonery (nothin heavy - no Breaking Bad or Sopranos...no Trainspotting!) The worst part for me was always thinking that something AWFUL was around the next bend - but it's usually pretty gradual: your SPLEEN ain't gonna suddenly RUPTURE in the night or something - it's just a gradual descent into shittiness - which you will be able to handle - then a gradual ascent OUT of shittiness, and hey, it is definitely doable, and you'll get through it - yay human spirit!!
And my advice is to stay off the pain meds if you can - I know in Canada that some Docs end up prescribing methadone for chronic pain (when oxycodone, hydromorph, etc become ineffective) - methadone is something I STRONGLY advise against. I spent 15 years on it, and it is crippling, LIFE-consuming stuff. All my advice here is from my experiences kicking heroin, NOT methadone - THAT was a different withdrawal process altogether (shudder). Don't get me wrong, I am NOT against opiates (I love 'em), but addiction is a rough road (altho opiates do not necessarily mean addiction - DAILY opiate use, sure). One of the pain Drs here where I live - a dr who used to OVER-prescribe narcotic meds - has had success managing pain with vitamin D supplements...Vitamin D, maybe some Vitamin MJ, and hey save them opiates for the rare occassions when the pain's just too much - or not.
Good luck bro