The tooltip text for the various Tender Stone items indicate that the refinement rate success bonus effect applies to the next refinement attempt you make.
This is not exactly true, however. The effect actually lasts for a limited duration (30 seconds for most Tender Stones, 15 seconds for the Tender Stone of Nine Divines), and players have discovered that, if they act quickly, they can apply the effect of a single Tender Stone to multiple refinement attempts.
This is not considered an actionable exploitation of game mechanics. However, you do so at your own risk.
This use of game mechanics is not the intended design of the item, and carries an increased risk of losing the effect before refinement completes, likely failing refinement (and losing the item).
We will not restore items lost to failed refinements, under ANY circumstances, if we can determine from the logs that the same Tender Stone was being used for multiple refinement attempts. Bugs, disconnections, or ANY other errors will not be considered valid grounds for restoring lost items in these situations.