I don't think there is any set rule as to how long a stage can last. I believe given individual circumstances it can be years. The stopping smoking, exercise and using proper meds under the supervision of a good pulmonologist can allow you to live and function well for years. For example, I was first diagnosed with COPD in 1999. I am now still able to have a fairly good life . I only use o2 at night and have learned to modify the rest of my life to accommodate the limitations I have. I feel the best thing you did was to stop smoking. I was a2 pack a day smoker for over 40 years. I quit 4 years ago and have actually seemed to have stopped my decline, at least for now. I hope this helps some.

There's no way of knowing. However, giving up smoking is probably the best chance you have of staving off rapid deterioration. Added to that, taking regular exercise will probably make you feel so much better real soon than you have actually felt in years.
There's no magic bullet so no cure on the horizon. All you can do is prolong your well-being by looking after yourself properly. Eat well, sleep well, take exercise, find the meds that best suit your condition and breathe easy. Best of luck.
By the way, now us a good time to start working your way down your bucket list.
I am loving my life opportunities and experiences. It gives me something else to think about rather than just feeling sorry for myself.
To be honest I haven't got time for COPD right now, it will just have to take its turn with all the other stuff that's queuing up to see me off.

unfortunately the damage is done but here's the good news staying Quit will help in breathing easier COPD rehab will help and teach the dos and don'ts joining a gym after completing rehab will also help in a big way to keep progression at bay as well as eating properly good luck

The better you take care of yourself the longer you live. I took my first PFT test in 2009 and at that time i had 39% of my lung function and had a recent test last month and it went down to 31%. and in the years in the middle I had exercised my tail off well what you can at stage 3 and it still dropped that much...but then again i did smoke for over 35 years... hope this helps in your search for a answer.

I really am not sure what stage I am at, but I do have a lot of exasperations. I don't exercise as much as I am sure I should, but when you are laboring to breathe, you really don't feel up to that. I smoked a long time and 2 years ago I was placed in a medically induced coma. I was in it for 3 months, not funny, in fact having a really bad time with the effects mentally and emotionally of that happening. PTSD for sure, I also had a tracheostomy so I do have a visible scar, (not a big deal to me at all)...but 3 months in a coma beats a nicotine patch for quitting !!!!!!!!!!!!!!!!!!! Just very depressed......I pray you have a support group i.e.: family. My poor daughter is my right hand, my family seems to care less. Never visit me, never call, it's so sad to be ill. So keep going......and my thoughts are with you.........