If the Formula 1 is the frozen cubes, I would get some tankwater into a small container, chop off as much as you think the fish will eat in a few minutes, put into the tankwater and then add to the tank. Just be sure you're not overfeeding.
Snails will often travel up to the edge and sometimes out of the water. In nature they are tidal zone dwellers used to being exposed to air for periods of time.
I've heard that the liverocks.com rock is pretty well cured when sold and there is very little die off during shipping. If that is the case then it should be okay to add it all at once. But, you may want to err on the side of caution and cure it when it arrives. Smell it when it arrives, if it smells clean then it is mostly cured. If it smells like dead or dying fish, or like a dried up bay then there is some die off going on. HTH