(1) I will party like a rock star on January 1, 2011,is dependent not only on whether or not I actually do party like a rock star on that date, but also on whether today (the day you are reading my statement) is before or after January 1, 2011. I don't agree.
We do not evaluate the truth of statements in a changing context. Thus, we evaluate the truth of statement (1) keeping mind when it was said, as well as who it was said about. The statement does not become false simply because I die, nor does it become false when someone else reads it.
That's probably more clearly seen from the use of past tense statements. The statement:
(2) I partied like a rock star,is dependent (for its truth) on whether or not I had already so partied prior to making the statement. The statement does not become true on January 1, 2011, if I so party then (don't worry, friends and family, I have no such plans). The statement was a lie when I made it, and it is evaluated in that context, not a changing context.
Let me add one point of clarification: we evaluate the statements within a fixed context, but the content of that context may evolve. For example, only God knows whether (1) is true (as of today), by January 2, 2011, a number of people will know whether it is true (hopefully, they will know it was false), but many of you who don't know me personally may never know whether it is true. Likewise, you may not know whether (2) is true, and if you cared to find out you would investigate my past, which would involve (in theory) an increasing collection of information upon which you could make your judgment.
The issue is mostly interesting because God knows the future. He can make true statements about what will happen tomorrow, and it is impossible for anyone to intervene to make God's statements false. This idea eliminates an "open" view of the future, and leaves Calvinism as the primary viable explanation for how human freedom and divine Providence are compatible (which is really a topic for another post).
Those statements that God could make (and on many occasions has made) are always true. God's promise that a Messiah would come was true when God made it, and remains true now, even though the Messiah has already come, because we evaluate God's statement from a single unchanging context.