I think the desission is yours.
I will tell you how we did it. I am no expert, I will just tell you what I did with my daughter.
Before 4 months: Infant stimulation cards, black and white cards, toys, books, check board,etc. You can find more info on this in Glenn Doman's book "How smart is your baby"
You can find review of the book at
www.childandme.comAt 4.5 month we started LR. The sessions are short, fast, full of great contents, no preparation. It made my life so much easier.
At 6 months we started YBCR program, 10 min a day (half DVD)
At 7 months TweedleWink once a day.
That is amount of screen time I was comfortable with. But the choice is yours.
Hope this info will help