My name is Alison, and I'm the Customer Success Specialist fro Ablestar apps. I'm sorry for the late reply on this, I realize your sale is probably over, but I though I would reach out so you have the information.
Our Bulk Editor app is capable of scheduling both the edit of the prices to start the sale, and then also scheduling the 'undo' to end the sale. You can read more about the process here: https://support.ablestar.co/article/30-running-sales-editing-prices-and-compare-at-prices.
The app also has a free version that allows for 5 free in-app edits and 5 free spreadsheet edits a month. If you have any questions or need help setting up a sale, you can reach us directly at email@example.com.