Hello Christopher. I am not sure what you mean by "when is it safe to start the renovations." Are you worried about the previous owners rights of redemption. I would think that you got information about that before you went ahead and purchased. What kind of a tax sale was it? IRS or property taxes? You should check with a TN attorney familiar with tax sales. Below is also a link to a website that deals with tax sales and redemption rights. You can scroll down to the section that deals with TN redemption rights. I hope this helps.
I purchased the property from the county in a tax sale. It's not livable. There is an tenant in one side of the unit. I did not want to renovate in fear that the previous owner could get it back and I not get anything from it other than ten percent more than what I paid.