There is no sandbox, in the sense that every new site is put in a sandbox. If you have sent too many signals relative to what is normal in your niche, then you will be filtered out for a while. IOW, don't get 10,000 links in a day with the same anchor text or anything else that seems artificial. If already in this filtered state, you need to continue working on the site at a more natural pace. You could be out in six months.