For a watch shipped with a movement that is not adjusted from the factory, yes, I'd agree. One should allow at least a month (I personally use 8 weeks) of constant run time to see if the watch settles in. While perhaps not true for every unadjusted watch, 2 of my 3 mechanical watches saw their accuracy change and settle after the first 7-8 weeks of run time. However, the Ginault is not shipped unadjusted from the factory. Ginault adjusts these movements and runs them for 6 weeks (I mispoke in previous posts when I said 6 days) and provides a test report with every watch indicating that it was running within chronometer specs prior to shipment. This "test and tune" activity happens after the movement has been cased, so there should be no inaccuracies as a result of the casing of the movement. There should be no run-in or break-in period with these watches. That would have already happened during the testing and adjustment period at the factory before they ship. They should be running very close to the values listed on the test report sheet out of the box.
From Ginault's webpage:
https://ginault.com/caliber-7275/Once a completed Caliber 7275 is encased in the watch, it will then go through a 6 weeks journey on our automatic winder to simulate real world use. Our watchmakers time each one of them every 7 days, then give each one of them a slight tweak if necessary to make the caliber to run even more accurately until it reaches as close as to 0 in the end of the journey. The mark “X” means the “average daily rate”. The Swiss COSC standard of this particular measurement is +6 / -4.We keep each measurement log in an excel file. When a Ginault timepiece is sold, we will provide you a copy of the measurement log with the caliber’s serial number, the actual power reserve tested, and the last measurement date printed on the copy.