how long is too long?

[Baldy]

This question has a couple different parts to it. This may seem a little strange, but I have a question regarding how long water can sit in a tank without fish or live rock.

Ive reached the point in my freshwater to saltwater conversion where i am ready to clean the sand and start mixing RO water to add to the tank. I have a 75G and will be mixing approx 20-25G of water at a time, and add it to the tank after placing the sand in. The thing is that it will take me probably 2 days to get enough water from my RO unit to start up all the pumps and skimmer, so is there going to be a problem with the salt settling out or anything?

after gatting everything running, if it ends up being a month or more before adding live rock, will this be detrimental? as well, after adding live rock, what needs to be done to maintain it between adding fish and inverts?

Sorry if this sounds like a newbie question, but i am a SW newbie =)