Reading comprehension's not the problem. The problem is that's a really bad way to communicate.
Just think if people spoke that way to people they knew. "Yeah, I'm coming to your birthday party, but that means up to and including one minute before it ends."
Do you talk to people like that? If not, why not?
I don't hold advertising to any lesser standard, especially as it's designed to get people to part with their money. If anything, it requires a higher standard of communication.