If you already have a cable line to your home then Comcast can usually get you up and running with the internet service within one to two days.
But if a Comcast Technician needs to come out and run a new cable line to your home from their service line then it can sometimes take a week for the Comcast Tech to be available for the job.
If you're moving you should order your Comcast Internet at least a week before your internet is scheduled to be installed to allow enough time for them to install the cable line if needed and activate your service.
The Comcast Tech should call you before they're scheduled to arrive at your home to do the install of the internet.
You can also access Comcast Hot Spots with your password and username while waiting to get your internet service installed.