From my experience, 6 - 8 month is about right .. yes, you ca start earlier if you want to try .. but if I were you, I would wait.
To cycle your saltwater tank, you need more than just a week .. if you have a fresh water, yes, 1 week may be enough.
If you have LR and LS, try cycle your tank 2 month before adding any live stock, especially if your tank is new. You have to give a chance for the beneficial bacteria to grow. Those invisible bacteria will help your livestock live span. Without them, it just like dipping them to a bucket of saltwater. It will be alive for only short moment.
Patient and you will be glad. Your LFS will tell you anything so you will buy because all they care is your money. The live stock die sooner, the better their pocket. How deep is your pocket?