In a nutshell, Boeing has admitted their backs are against the wall as they currently understand the situation before them. They expect to have all four RR
-powered 787s into the air no later then January 2008, which they feel will give them sufficient time to perform the necessary flight-test and flight-certification duties to achieve their production certificate for the 787 and deliver LN0007 on time to NH
in May 2008. The two GE
-powered 787s will be doing mostly GEnx-related certification work so they're not as critical to the program.
Boeing has already completed much of the non-flight-related testing and certification. As such, the four flight-test birds won't need to do as much as previous airliner program test birds have had to. Also, these 787s will not be doing as much airline route-proving and PR
work like the first A388 birds did, so they'll be spending more of their time on certification and test. And Boeing intends to operate these planes "24x7, 7 days a week", so they will not artificially restrict their testing to daylight hours when not required to do so.
As such, Boeing feels they can still pull it off. Their next update is October, so we'll know more then...