Starting patrols before Sept 1, 1939?

Prior to the British declaration of war on Sept. 3, 1939, approximately 26 front-line u-boats were on station west of Great Britain and Ireland. To do this they would have sailed prior to Sept 1, 1939, most likely around August 20th to 25th at the latest.

Therefore, my question: is there any way to start a patrol prior to Sept. 1, 1939; early enough to be on station west of Great Britain before the Sept. 3, 1939's declaration of war. Leaving port on Sept. 1 (the earliest game time that I know) just doesn't allow enough time.