That's a great question! The unlimited boosters that you have and the remaining time the are available for should show up in the upper right of the graphic that appears when you're entering a level.

If you don't see the icon in this graphic when beginning a level and you should have a timed booster, please open a support ticket through the support link in your app. We also ask that you include a screenshot of the start-of-level pop-up so we can look into this further.

This link will help you take a screenshot for your device: