Niko is right. This is the best time to add your LR. However I understand you delima in that you are wanting to buy locally and want to ensure that you are getting choice rock. So here several alternatives.
1) If the rock is cured and the pet store isn't that far from your house, as long as you wrap it in wet newspaper and then a heavy duty garbage bag, it really should be ok. You might have a little die off but you should be able to place it directly in your tank. Thats what I did with that arched show piece and it traveled an hour. But the key here is that it "HAS" to be cured. So it kind of boils down to how well do you trust your LPS.
Well we do trust the one that is farthest away from here but they give us the rock in IO 5gal buckets with water in them from there displays. That way they don't dry out.
2) Go to Wal-Mart, Target, Pamida whatever is local to you and get a large sized rubbermade container and cure it in your apartment until its ready to put into your tank. To cure simply add the appropriate sg saltwater and completely cover the rock, a heater, a powerhead and change the water every couple of days. Readings of 0 amm and 0 nitrites will let you know when its cured. I've also stuck a cup (and left the cup in the water) of Live Sand from my tank to help speed up that process.
We are planning on getting one for aging our water before putting it in the tank. I guess we can get 2.
3) Buy your live rock and add it to your tank, but don't add anything else for a while until you get your live rock built up. Once you have all of your live rock in your tank and arranged how you want you can start buying your livestock. (I mention this last as it is probably going to be the least favorite choice)