We had something similar happen, so I understand your concern. In our case the original plan was to actually build o top of our freehold house. The plans were ridiculous, but still had to be looked at & approved or disapproved by the town planners. The Council could have passed it, even though they legally had no rights to build on top of part of our roof. It's a crazy system.
What we learnt by going through it & talking to surveyors & solicitors etc, was that property developers always start off by putting in ridiculous plans, knowing they will get rejected & softer plans will then be accepted. It s sort of a game of the trade.
You need to find out if plans have been submitted to the councils town planning department. You can ring them up with the address, but given your close proximity to the build, you should get an official notification & invasion to place your objections to the build.
The time does sound excessive. They did far more to the building next door to us & it was over in 2,1/2 months. 8/9 months makes the cynic in me question what they are really up to. Who owns the top flat?? Is it the freeholder ? Are they planning to build more flats on top, rather than just an extension?. You need to see the plans which will be online to view at the councils town planning website. Would making your low rise block affect your property value, more noise from more people trapping up & down the block etc.
Party wall law dictates that the property developer pays for legal advice for both of you & an agreements drawn up. You can insist on reasonable changes etc to protect your rights, including writing in a clause that means you get compensation if they go over the promised time scale. This makes them work to time. Also times of works etc. There will be local laws on this, but check if they are compatible with the hours you get up etc. if you normally get up at 8 am for example & the law says they can start work at 8, you might want to ask them to start at 7.30, which would be reasonable as it's only slightly different. You can ask fir extra expenses to be covered such as calming plug ins for your dog & also that they keep a way clear for your dog to safely use your garden.
Your disability gives you extra protection, any neighbours with kids can also cite 'protection of children from harm" in their objections to the planning application. But excessive noise, blocking out light, effect in your home life, parking & rubbish disposal in the area, if you will be overlooked by the new floor or extension are all things you can object to.
If it gets messy, as our situation did, you can contact your local councillors for help. Ours was a big help & it worked out well in the end.
For now though it sounds like your freeholder is sounding you out before putting in any plans