I wanted to confirm that I have noticed that this projector does in fact take about 30 minutes to come into full focus, and I have a simple procedure that can prove it to you.
One way to test this is to get something on the screen that requires the full resolution of the projector. Movie material is obviously completely out of the question, and honestly most focus test patterns are pretty much worthless too because they were made for old CRT-type displays that were not as capable. I found that the period in the Windows 7 icon font (Segoe UI 9pt) is a good item to use to see the pixel structure. It consists of two vertical pixels.
When your projector is properly focused and the convergence is right these two pixels should appear razor sharp as two discrete white pixels directly above each other no matter where they are on the screen. Since my screen as a slight bulge in the middle (don't ask but it's about 1/4" higher) I cannot perfectly adjust both the center and the edges the same, but I can find a perfect medium where both are reasonably sharply adjusted (sharper than my old projector could at any point at least).
After the projector has been off for a day and I turn it back on, the focus shifts such that the edge period pixels become super focused and the center period pixels are blurred so slightly such that I cannot see the pixel structure clearly. The reason the two locations are not equally affected--granted this is my THEORY at least--is because, again, I have a slight bulge in the center. It takes a full 30 minutes for the two locations to equal out and become as they were when I turned off the unit, with both being well in focus.
The point is that the instruction manual is right when it says the unit requires a full 30 minutes to heat up for focus adjustments. If you do not wait that length of time, you will be focusing for the heat up period and not the steady state.