I found that working on the PC muscle on my drive to and from work had been very successful for my premature ejaculation.

Here is my routine that you can follow and modify to fit your work schedule:
I would hold my PC muscle for as long as I could and release. Then I would take a brief 3 second break and repeat the clench again. I would do this from the beginning of my drive when I left the driveway of my house until I reached the parking lot of my office building. On my return from work, I would start at the parking lot of my office building and continue until I reached the driveway of my house. I would do this Monday through Friday only. The weekends were my free days (rewarding myself for my completed hard work).

Feel free to modify my schedule and let me know how it goes for you!