As it is Harron Homes, you should expect no end of problems getting anything attended to after you have moved in based on the experiences of buyers who have posted on this forum.
The fact that their Customer care department just
"pass you off to the site sales" rather than the site manager who would be arranging any required works, just demonstrates they really haven't a clue.
So it is even more imperative that you get your home professionally and independently snagged BEFORE you move in. I would recommend
www.brickkickers.co.uk Bearing in mind it is Harron Homes, I would advise against legally completing until all the snags and defects have been attended to. Instruct your solicitor to not legally complete until you say so.
Regarding how long it will be before you move in is a moot point. They usually have to give you 14 days notice (10 working days) normally after the NHBC issue the CML certificate and final inspection. This however, does not necessarily mean your new home is defect free!