Every tank is different so it is hard to give a time frame but as soon as it has cycled and is stable it is fine. If you are new to saltwater then I would say take your time and make sure you are able to keep fish alive for awhile first. When you have a better understanding of maintaining a reef then get the anemone. I would recommend the BTA as they are very hardy and accepted by most clowns.
When I worked for a maintence company I would set tanks up with live sand, cured live rock, and aged saltwater and then place fish, corals, and anemones in it that same day. There are no issues as long as everything is cycled and you do not overstock.