(informal, chiefly law) In the event that the thing being discussed comes to pass.
1944, Thomas Reed Powell, letter to William O. Douglas, quoted in Melvin I. Urofsky (1989), '"Dear Teacher": The Correspondence of William O. Douglas and Thomas Reed Powell', Law and History Review 7(2), page 364,
No one cares about what a judge thinks, if, as and when. All that counts is what he says.
1988, Harry Brown, A Walk in the Sun, →ISBN, page 75:
The whole thing, Tyne decided, would make a nice problem to mull over in his old age -- if, as, and when.