I Have Been On Paxil For 25 Years And My

I have been on paxil for 25 years and my heart doc wants me to take Bupropion HCL 150 mg 2 x a day. T o help me quit smoking. At first I was takeing both, then upon picking up my 2nd rx the pharm. ask me if my MD knew I was taking both. I have since then went to my doc and have been weining myself off paxil and started today taken the other pill, What I'm asking is how long will my withdrawl from paxil take ?