Did Dumbledore ever explain exactly when his plan became "martyr Harry"?
I admit it's been a while since I've read the books, so my info may be faulty, but the feeling I got was that he didn't really plan that. I don't think he expected everything to happen as fast as it did.
We've already discussed how First Year was a ploy to trap Voldie's shade with his own desire, and Second Year was a Malfoy plot, and Third Year was the culmination of a thirteen-year-old comedy of errors.
The point where Dumbledore probably gave up on letting Harry live a normal, happy life (to the best of his knowledge) was the fiasco with the Goblet of Fire. When an ancient, powerful artifact broke its own rules to put Harry in danger, he (rightly) assumed it had to do with Voldemort, and decided that Fate couldn't be fought, and started preparing for the next war. When Voldemort came back, he tried to drum up support, but old wounds were still fresh, and no one wanted to hear about the Wizarding Boogeyman come back to life.
This point between Fourth and Fifth year was when he started up the old Order again, I think. He probably knew about the DA, and simultaneously was happy about how Harry was preparing his students and saddened by the fact that it had gotten to this point. At this point, most of the original plans are in shambles, most of the Wizarding World is uncooperative, and the timetable had been moved up. Then comes the Battle at the Ministry, and Dumbledore again wins a somewhat phyrric victory. The Ministry is forced to recognize the return of the Dark Lord, at the cost of the one person Harry thought of as true family, his godfather.
Again Dumbledore is at odds with himself, hurting because this boy he watched grow up is in such pain, sickened that he considers that day to be net plus, and hopeful that something can be done with the aid of the Ministry. He settled some affairs for the summer with the Order, and went Horcrux-hunting. Having found the Gaunt ring, probably entranced by the Ressurection Stone, he puts it on his finger, and becomes lethally cursed.
Being the biggest wrinkle in his plans yet, which is saying something, he starts to put his affairs in order, giving Snape the orders to kill him should it become necessary, orchestrating Occlumency lessons for Harry (that didn't take), and taking Harry to the one other location he knew about, to set Harry on the path to finish his work after he dies. He leaves all the clues he can in the only way he can, in a way that seems perfectly innocuous to any spying Death Eaters. The Light-Out, the Snitch, and The Tales of Beedle the Bard, if my memory serves. At any point before his reappearance at Heavenly Kings Cross, I'm not sure Dumbledore ever knew about Harrycrux.
Again, it's been a long time since I've read the books, so I might be wrong, But I don't think martyrdom of any kind was in his plan, before his curse, or even before he died.