If there's already an internet or phone cable attached to the house then it may only take a few days to get the internet service up and running at the new house.
But if the ISP has to install a new wire or fiber optic cable to the new house and then install the box and equipment outside on the house then it may take a few weeks.
If it's a new house build and you plan to move in soon you should call the ISP a few weeks before moving in to allow them time to get the internet service installed to the new house.
If it's just a house you're moving into then also give them a few weeks notice so they can install and activate the service and have it ready as soon as you move in so you won't be without internet service.