We know that he spent his last two months in "the house that Medly's Mist-E-Rub built", between Lake Brandt and a "five-acre private lake".
"You said he built the raft. How long has be been here?"
"Two months. We meant his leave to last only a few days. But you see, he doesn't seem interested in going on with his education."
But he had a three month leave, as we see from:
So that's why you brought me here, thought Ender. With all your hurry, that's why you took three months, to make me love Earth. Well, it worked. All your tricks worked. Valentine, too; she was another one of your tricks, to make me remember that I'm not going to school for myself. Well, I remember.
And also from what Admiral Chamrajangar tells Graff:
"Took your time, didn't you, Graff? The voyage isn't short, but the three month vacation seems excessive."
So where did he spend the first month?