The question I get asked most isn't where to go, it's when to decide. Here's the short answer, and it holds true all year round.
For Easter week: November. December is already late for the good options, and January is too late altogether. It's a narrow window because you're competing with everyone else at once.
For August: March. It's the strictest of the three. Safari camps have a fixed number of beds and don't grow; once they're full, the alternative isn't a similar camp, it's a worse one. Nearly one in three trips I design leaves in July or August.
For Christmas and New Year's: June. It sounds excessive, and it isn't. A house with its own chef in Lapland for New Year's Eve books up over the summer, just like the best safari dates.
Outside those three windows there's more room, and a good trip can still be put together with a month's notice. The only thing that changes is what you're choosing from: with six months, everything; with one, whatever's left. Sometimes what's left is excellent. Sometimes it isn't.
If you have a date in mind, tell me which one and I'll tell you whether you have enough time.