I started my LO after around 16 months I believe and after a few vieweings, she was bored or rather distracted by all the fun things to do around the house rather than sit and watch the videos. So after a week or so, I started showing the different videos and didn't worry about the schedule since, if she wasn't watching them, it didn't matter anyway. She watches videos on a small portable dvd player, so we also took it with us in the car when she had no choice but to sit and watch it,
. Since we started late, I wasn't pressed about sticking to the schedule and just decided to show them when she showed interest. She still picked up a lot of the words suprisingly. Now, I show them at random so she doesn't get bored or wait til she seems bored with all the other things to do around the house to show the videos. I know your grandson is a bit older but maybe that will help.