I wouldn't bother.
There's 3800 houses being built just down the road from me, about 15 have moved in.
I clean the sales suite, showhomes and sparkle each plot the day before the move in.
I know all the move in dates for the next 8 weeks in advance and could quite easily be picking up all these houses as the customers move in.
I don't because as stated, every window cleaner in town will be jumping at the bit to pick up these houses, leading to a price war. These houses will be canvassed the sh!t out of over the next few months, you can guarantee that.
Also being on site the windows will get dirty very quickly. In dry weather windows on site can look dirty just a few hours after being cleaned with all the dust.
Another thing to remember is that alot of the 'new' windows will probably have scratches on, left over bits of cement or silicone. Your better off letting some other mug either take the blame for the scratches or get the windows up to a decent standard, before you jump in and offer your services at a later date.