LIGO calculated the maximum delay of the signal, 10 ms, by dividing the great-circle (!) distance between the two sites, 3002 km, by the speed of light. This is an incredible sloppiness, and not only LIGO but all triumphant professors are silent about that. It seems only Hilton Ratcliffe has the courage to publish something on the matter:

http://www.newkerala.com/news/2016/fullnews-23659.html
"On September 14, 2015, the LIGO (Laser Interferometer Gravitational-Wave Observatory) observed a "chirp" lasting about a fifth of a second (GW150914). Analyses of the signal suggest that it was produced by the cataclysmic collision of two black holes a billion light years away. This was probably the verification of the most dramatic prediction of Albert Einstein's General Theory of Relativity. Accordingly, we ought to have a critical look at the relevant experiment before we finally incorporate this great achievement into the body of scientific knowledge. (...) There is also something which appears to be too fortuitous about GW150914, as noted by the distinguished Indian astrophysicist Dr. Abhas Mitra: Given that the radius of Earth is 6,370 km, we can calculate the linear distance between the LIGO detectors at Livingstone and Hanford at around 2,500 Km. Because this distance is absolutely negligible compared with the distance to the origin of GW150914 (1.3 billion light years), both detectors should see the event almost simultaneously. There should be a delay of a few microseconds at most if both detectors received the signal from the sky above. However, the actual delay of seven milliseconds was very much larger, and is possible only if the source was almost perfectly aligned with a straight line joining Livingstone and Hanford."

Perhaps Ratcliffe and Mitra are exaggerating, but then why isn't there any precise calculation coming from LIGO? From triumphant professors? A good explanation is this:

When the results are all fake, precise calculations should be avoided - they can only expose Achilles' heels. In such cases one should only be careful not to fabricate suspicious (unrealistic) data.

Pentcho Valev