From what I've read on other forums, you don't have to install the software. In fact, it may be better if you never install it. When you call to cancel the customer service rep will see you never even signed in, so they'll let you go pretty easily.
And for cancelling, I'd wait a little longer then 5 days. Its a 45 day trial, so I'd say give it maybe 2-3 weeks. I've never heard of the company giving anyone problems for cancelling too quickly, but I'm all for playing it on the safe side. Especially when you have such a long trial period.
I'm did the AOL offer myself when I joined for my flatscreen, and I'm going to cancel next month. Around day 30ish or so...That might be a bit long, but I'd say wait maybe 2 weeks.