im new.

so once i get my nano cube and i add in the live sand and rock, how long do i need to keep it running so that its cured? a friend of mine (whos had a saltwater tank for 3 years) said that if i buy pre mixed salt water from the pet store then i only need to wait 3 days before i can drop any fish, but another friend of mine (one month of saltwater tanking) said he waited 3 weeks before he added his clown and it died. he said you need to let your tank cure for about a good month before you add anything.

I dunno what to do.....?
advice?

do some read up on nitrogen cycle and you will know what cycling and curing it's all about.
curing liverocks is merely the process to cleanse the die off from the liverocks (there are bound to be some when the liverocks get exposed to air). the die offs will start the cycling process for you where it will be process from Ammonia(very toxic),nitrite(still toxic) to Nitrates.and from there the nitrates can be furthur process to nitrogen and release as air bubbles from the sand bed or liverocks.

as to how long the process takes,u will need to buy test kits to test the water. in the initial stage u will see high ammonia level which will drop to 0 and yr nitrites will rise. once this taper off to 0,u will have nitrates reading. wait till the notrates gets to 0 or at single digit reading before u introduce livestocks. what yr tank has achieved now is an equilibrium where the bacterias are sufficeint to process the waste generated.

u will still need to stock slowly as every new livestock will create a small mini cycle.

I had a person from my local fish store set up a 180 and had fish in the tank by the end day.