If this is a new installation then it will change every day, the idea is that it might be complete by the time the internal connection is due. I say might because if there are things in the way (such as blockages) then the whole installation may be pushed back.
Thanks for your post and welcome to the forums. It's really great having you on board with us.
The pre install visit will act like a floating appointment. We try and do them in advance but these can be done anytime up till the day before your install. If we have some spare availability in your area before hand though we will come sooner.
This is nothing to worry about though. If you have any further questions then let us know 🙂