Your PhD really shouldn't take 6-7 years. Realistically, the Masters should cover all your course requirements so the incremental time should be 1-2 years. At

Your PhD really shouldn't take 6-7 years. Realistically, the Masters should cover all your course requirements so the incremental time should be 1-2 years. At least for a CS PhD in the US, this is not the case: even if you enter with a Master's, finishing in 4 years is usually typical. Of course, it depends on the school, area of study, adviser, and the student.