Lol, obviously the estimate will depend on the current speed. If that speed shoots up, the estimate will go down and vice versa, so unless that speed you have is your average daily speed, I don't think you have to worry about anything.
I'm on a DSL connection at home with a 2-3meg connection. My downloads can go up to 400kbps but my average is about 250-300ish. A full install takes average 4-6 hours, but I have other obligations in life like work, family, personal hygiene, etc. so this "delay" isn't too big a deal. Usually, I have the full install downloaded by Day 2 after release, and it'll take me a few more days to get round to installing it and tweaking it to my preferred settings.