There are a number of questions which need to be resolved before we can sensibly approach this subject. Either that, or we can degenerate back to the status quo of speculating. Here are the first 2 of a series of such question and answers which I will post on this thread. All sensible alternatives are welcome.
Q1: How far was Titanic from the turning point of The Corner at Noon, April 14, 1912?
A1: The Calculated distance to run from Daunt Rock departure to The Corner is exactly 1673 nautical miles. The distance is made-up of 55 miles from Daunt Rock to 1 mile south of the Fastnet Rock, then 1618 nautical miles on a Great Circle course to The Corner.
According to 3rd Officer Pitman, Titanic had covered a total of 1549 miles since FaoP...Full away on Passage...at Daunt. That left 124 miles, not 126 miles left to run at Noon, April 14.
Q2: Captain Smith determined the time of 5-50 pm as when to turn the ship. To do so, he would need to assume an average speed over that time. So what speed was used between Noon and the turning point?
A2: Titanic averaged 22.1 knots between Noon, April 13 and Noon April 15. However, unless exactly the same conditions expected after Noon as before it, Captain Smith would revert to a speed indicated by propeller revolutions per minutes... in this case 21.5 knots at RPM of 75. At that time, they had yet to calculate Slip Tables for Titanic.
Like Captain Moore of the Mount Temple and Titanic's 4th officer Boxhall, Captain Smith would expect to meet an easterly setting current of about 0.5 knots near The Corner. Not immediately after Noon but certainly between 3 pm and the time of the turn. It is inconceivable that Smith, like any other experienced Navigator familiar with that part of the ocean would not make allowances for such an event. Consequently, I suggest this is how Smith worked his ETA The Corner.
A...Noon to 3 pm at 21.5 knots...64.5 miles.
B...3 pm to 6 pm at 21.0 knots... 63.0 miles
Distance steamed by 6 pm........127.5 miles (6 hours steaming)
Subtract distance to go............... 124.0 miles. (from Noon)
Difference.........................................3.5 miles.
3.5 miles at 21 knots = 10 minutes...!0 minutes from 6 pm = 5-50pm.(5 hours 50 minutes steaming from Noon).