I have name changed for this. I have experience of codeine withdrawal that may be helpful to the OP.
At my "worst", I was taking 72 Nurofen+ a day, in 'doses' of 8 tablets (so just over 100mg of codeine) at a time. My life revolved around driving to different pharmacies to buy them, cringing with shame each time I asked for them, dreading the odd occasion when the Pharmacist would refuse to sell them to me. It cost me an absolute fortune, got me in serious financial trouble, made me incredibly sly and secretive, and I ended up with a gastric ulcer which burst in the middle of the night and I then had a week long stay in ITU. I was very unwell.
When I was discharged, I contacted my GP and they agreed to prescribe me large quantities of codeine, so I could taper at home. I had been addicted (on and off) since I was 21, and the ulcer burst just before my 42nd birthday.
I initially cut my doses down to 4 times a day, but kept the dose at 100mg a time, and I didn't have any physical withdrawal symptoms to begin with. I cut down by 15mg per dose every 3/4 days, so around 3 weeks in I was taking 30mg 4 times a day. I then cut out one dose per week for 2 weeks until I was taking 30mg twice a day. That was when the physical symptoms kicked in. It wasn't too bad to start with, some nausea, lack of appetite, irritability (which was tricky, as I didn't tell anyone other than my Doctors about my addiction), and the worst of the symptoms; sweating, restless legs and the total inability to sleep. It was horrific. There were a few times when I just couldn't stand it, and ended up taking some extra just to stop my legs from feeling like they were crawling with ants.
The jump down from 30mg twice a day to 15mg twice a day was hard, but more psychologically than physically at that stage. I had relied on codeine to make the world ever so slightly softer and easier for virtually my entire adult life, and it was like coming out of a calm, quiet room into a busy train station. I was totally overwhelmed, and it was at this point I realised I needed to talk to someone about why I'd starting using codeine to ''take the rough edges off my life", rather than for pain relief.
I spoke to an excellent Therapist, and I continued with the 2 doses of 15mg a day for 6 weeks, while I worked through the psychological issues attached to my addiction. I was then able to go down to 7.5mg twice a day (at which point it was having no discernible physical effect, it was only the psychological dependency remaining). Then 7.5mg once a day for a week, then none.
I still had 10 x 30mg tablets left, and a couple of weeks after stopping completely, I had a really shitty day, and that little addict voice in my head said "Ah, go on, you deserve to take the edge off, you've earned it!" and I took 60mg in one dose. As the familiar feeling flooded through me, I got really scared, and realised how stupid I had been, as I could see that I would immediately be hooked again, and back in the old, familiar, lonely cycle. I crushed the rest of the tablets and washed them down the sink. I felt a flood of relief that they were gone.
Sorry, that was long! My experience was that the worst of the physical withdrawals lasted around 5 days, but the psychological withdrawal was much longer. Even now, years later, I have days when I think "I could just buy one packet..." I'm not sure if the psychological dependency will every be truly "gone" for me, I was addicted to those little bastard tablets for such a long time.
I really feel for anyone else who gets "stuck" on codeine, it really is a total arsehole of a medicine, far too easily available, and far too easy to get addicted to.