You probably heard it before
-- but it really depends on your baby, follow with his interest but be ready to stop
before he gets bored
With my last baby, at that age we did 2 sets of 5 words with just a couple of minutes break for cuddles and kisses
Then another 2 sets may be 20-30 minutes later ( it was not regimented, I just made sure we will get up and either dance to classical music or look at some colorful pictures on our walls or do some balance exercises) At 4 months we started Little Reader, as he was really ready for it and loved it more then I can describe!