Shouldn't be a problem. I had my tank set up on one Saturday I think it was, with the water. I added the sand a day later I think, and the rock wasn't added until the following week because I didn't have a heater at that point. So, it was a week after I put the water and sand in for me, no problems.
As for the quantity of rock, if you're cycling your tank, get as much rock as you can in one shot, that way you don't have to worry about getting more later, curing it before it goes in and then trying to add it to your current rock structure and having to rearrange it with fish in the tank. The more you can do before you have fish/inverts in the tank, the better of you are.