Rather than skipping the W3D3 workout, just do it asap and slide the routine back. To regain some of the fatigue you've lost by skipping a day, you might consider doing W3D3, day off, W4D1, day off, day off, W4D2, day off, W4D3 and than take it from there into week5.
This stage of the program is mostly about building up fatigue and so completly skipping a day could cost you most of your benefits, especially if it turns into a 5-day period with no workout. Your body will recover from the fatigue you've already acrued and then you'll be going into week4 too fresh to get best benefits from it.