Under normal situations, the Galaxy Note 5 would launch sometime this fall, as Samsung has done in the past with its oversized handsets. But these are critical times for Samsung. After being stuck with excess Galaxy S5 devices, Samsung reinvigorated consumer interest in the Galaxy line by redesigning its flagship phones for a more premium feel. Thus the Galaxy S6 and Galaxy S6 Edge were born, and while the overall reaction has been positive, sales have suffered in part because of shortages to the curved screen Galaxy S6 Edge.
As for the Galaxy Note 5, it belongs in territory that Samsung helped pioneer (phablet) and, for a long while, dominated without much competition. However, Apple took a gamble on big size devices with the iPhone 6 and iPhone 6 Plus, the former with a 4.7-inch display and the latter with a generously sized 5.5-inch screen, just a hair smaller than the 5.7-inch display on Samsung's Galaxy Note 4.
Timing is key. Apple unveiled its enlarged iPhones less than a week after Samsung introduced its Galaxy Note 4 last year, then offered them up for sale weeks before the Galaxy Note 4 hit the market. That gave Apple the competitive advantage.
Samsung is looking to switch things around this year. A move to mid-August would give the Galaxy Note 5 a lead time of several weeks before new iPhone models become available, assuming Apple doesn't do the same thing.