I am not a Comcast Network Engineer. I am just a moderator relaying messages to them. I am not the one to answer your question. However, I will split your post to a new topic since it is actually off topic here.
how long is expected? I only ask because I need to change my girlfriend's current modem with a SBG6580 so she can save some monthly rental charges. Will she be down for a few days or months?