I don't think you need to wait. Some sand dust seems less problematic for the fish than being crammed in a little tank.
You can add sand whenever you want to. You just need to rinse it well, which makes any extra $ you spent on live sand kindve a waste, but there's probs lots of bacteria on your rock anyway. It's a pain to rinse, you can use tap water and treat the last round with chlorine drops. Helps to run a filter sock for a day or too after as well. Some people find it less dusty to use a wide PVC pipe and funnel to send the sand right to the floor of the tank instead of pouring it in and having it blow around.
I prefer to add sand a few weeks after everything else. As the rocks settle in they produce a lot of detritus sometimes, bare bottom makes it easy to remove that. I never get the scape right the first time either, so no sand makes it easier to change up. Also if the rocks leach phos it's easier to dose LC barebottom. I'm running my second tank without sand right now until I feel like adding it. I have a wrasse that needs to sleep in the sand, so I put a little old sand in a Tupperware for his bed, I figure it's seeding the rock with some worms and stuff too.