Three weeks for me. One of the things that I forgot to ask before surgery was about how the incision would be closed. on seeing it for the first time, I was a little surprised to find it covered with what looked to me like Saran Wrap and with no stitches at all. I was careful of mine also and never tugged on it as I, too, was a little afraid of opening it up. After I got home, I never scrubbed the area but just sort of dabbed at it with the antibacterial soap. While taking a shower on day 20 after surgery, it just disintegrated. I didn't actually notice it was gone until I was drying off and found just my skin with a simple line down the chest.
The basic guide line is that the incision should be healed over by the end of the third week. After that, you should be able to scrub the area as much as your skin will tolerate.
Larry