Konami Digital Entertainment has released their latest financial report, which includes sales data and planned releases. Metal Gear Solid V: The Phantom Pain is listed under ‘Q3 releases / Pipeline’. In this case ‘Q3 releases’ refers to the third quarter of last year’s financial year (not to be confused with the calendar year), and ‘Pipeline’ to upcoming releases. So the schedule covers both the releases of Q3 2014 as well as the games planned for release in the first half of this year.
According to some people, this could mean the game is planned for release between April and June of 2015, as releases past this time frame aren’t covered (for a more detailed explanation see Arkham Inmate’s post on NeoGAF). Of course, this is just a theory and not a confirmation, so be aware of that, but the release window does seem plausible. The official announcement confirming the release window should come soon.
As for sales data, here you can see the Metal Gear series moved almost 2 million copies in FY2015 Q1-3, which ends December 2014.
The report also mentions ‘solid’ sales for MGSV: Ground Zeroes on Steam, although no exact numbers were given.