Not to mention that the clock starts ticking on the first prop inspection. There are calendar-based as well as operating hour-based guidelines for sending it to the shop for an inspection that every manufacturer has. My Whirlwind prop listed 650 hours or five years, but they all vary somewhat.
After the calendar time has passed, they'll replace O-rings and seals as well as inspect for corrosion (at a minimum), even if you don't have the first hour flying on it. Yes, that happened to me when I bought a prop on a group buy here. While I did get a good price, that was eroded away with the first inspection that ran about $1K.
You'll need the prop to fit the cowling, but I wouldn't be in too much of a hurry to buy one prior to that.