Hello,
1) Are you sure that you added that to the short description? Provide us with link to product where you added that, please. Because I tried and it worked for me.
2) You can switch product type to simple, set the sale price and end date, save changes, then switch back to variable product type (your variations should be ok even if you switch to simple and then back) and save your product. Check if the timer appears after these actions.
Regards