I Babysit My First Grandson, Who Is 8months Old. He's

I babysit my first grandson, who is 8months old. He's sitting up, creeping, and starting to crawl. I try to abide by the strict rules that his parents require. Recently, because I Heard that their pediatrician gave the okay, I bought an exersaucer. I only put the baby in it for 5 minutes at a time, maybe 3 times during the entire day. Now, his mother tells me that I can't use it at all because it will delay the baby's walking. She says that the bouncing is the main problem. I don't get it. What do you think?