I still can’t find the answer to this question. I have five chests and the timers never go down..

When you select the chest, at the top of the screen the display bar gives you information about the chest. In that display bar you will see a button with a number time on it, click on the button. If done correctly the item in the merge box area will now display a shadowed clock with a sliver showing a countdown has begun. Only one chest may be activated in this way at a time without spending the required amount of gems to instantly open the chest. I hope this helps.