From my experience, 30 minutes will not cause much of a die off. About a month ago, I put 20 pounds of cured live rock in a 55 gal tank. I never got an ammonia reading above .25 after adding it. When I later added another 15 pounds (again with the LR out of water for 30 minutes - aka the time it takes to drive home), I never got any ammonia spike, I'm guessing because the bacteria in the first 20 pounds were able to eat up the small amount of ammonia from that later die off.