"Stays in the Google Sandbox can vary from one to six months, with three to four months being the average time frame. Less competitive searches will be given the much shorter stay in the sandbox, while hyper-competitive keywords will often spend six months in the sandbox. The filter will be gradually decreased over time, and will lose most of its dampening effect in about three months. However, for the most competitive search keyword phrases, the Sandbox filter might remain in full force for six months." (http://www.google-success.com/what-is-google-sandbox-effect.htm)
I haven't experienced sandboxing myself, but I guess every particular situation is different. Hope you get out of it soon and well!