About a day or two.. less than a week is okay for me. But the thing is, between those days, I'd reviewing what I have done, Leave comments in the code and change some variable names as I read through. No major changes though just patches. So during this time I don't code (a little) but I look at the next project.

For me, I don't really take a break here in japan. In Japan, the working culture is totally different than other countries. But it's a 2 days break offered by the office after working 5 days a week, 12-14 hours a day and after finishing the project they told us to take a short break.