I did the CPL part time over a period of 2-3 months, and it didn't take any longer hours wise. I think the important things were to not leave too long between training flights and have a flexible job and training school. My job and flight school were really flexible, so if the weather looked like it might be poor at the end of the week I'd fly early in the week. They would occasionally teach after hours if I could escape work earlier. Also important not to stagnate between flights, if you can, take training material to read at work just to keep you in the right frame of mind.
I took unpaid leave for the ME/IR as I figured this would need more commitment, but in hindsight I could probably have done some of this part time, but not as much as the CPL.
Be aware though, if you are not careful I know of people whos work commitments have taken priority and getting the licence and ratings has dragged on for too long, they then start spending more money to refresh themselves.