My LPS just got in some tonga i opened the box and it look realy good how long should it be in the the pet shop untill i can buy some. so it will not spike the tank. i have a 75 with a 10 sump.
You can cure your own rock in a clean container with a powerhead and a heater. This way, you get to pick the best shape, and you may save more critters on the rock than your LFS would.
Considering it's only a small amount of rock, I think I'd grab it now while you've got the choice picks and cure it in a trash can for a couple of weeks as Jimmy suggested. JMO