I'm not sure anyone on here can give you an answer to that, as it is going to depend on a lot of factors. For example, what infrastructure already exists and what needs to be put in, how busy the installers are, how many other orders are going through the system etc. etc. For a start, if new infrastructure needs to be put in that's down to Openreach, who are a separate company and nothing to do with this forum.
Your best bet is to ring and ask. If you do it early enough, you may be able to pick a date. Leave it too late and you may not get the time you want if they are busy etc.
