If you have live stock already inside the tank, then putting in uncured live rock will kill whatever is in the tank. The decaying organisms on the rock will rot off and pollute the water, therefore giving off ammonia. If you still want to get the uncured rocks, then it's best to cure them in a seperate tank or bucket of salt water. Depending on the rock itself, it could take as fast as a week to three or four weeks. Just let it sit there in the bucket, fully submerged.
I think it would be better to just spend a little more and get the cured rocks, but make sure they are really cured by picking them up and taking a whiff. If they smell a bit like rotten eggs, then they are not fully cured. Buying cured rocks will also get you started on this hobby a bit quicker... we all know patience is a virtue but when it comes to fish tanks we would all like the perfect tank in the shortest time possible

. So take your time with the hobby as you will be rewarded in the end.