Didn't Baldwin just spend a ton of time doing a half-hour podcast for WNYC? A half-hour talk show makes perfect sense for Baldwin, especially given how close he is with Lorne Michaels.
People are thinking that the show will actually be his podcast, which has developed a following. The late hour will allow for more content freedom, and the show would all Baldwin the freedom to take other projects like movies or guest shots on other tv shows...
And remember that after the end of 30 rock, NBC signed Baldwin to a two year "overall development" contract, paying him to basically not work, and that it was Lorne who pushed for it. The thinking was that it was to retain him while Leno's contract ran out, and they executed the "late night shift".