The Cancel Time slider controls the amount of time you have to cancel a purchase when using any features that cost flutterbucks such as laying eggs, hurrying eggs, moth or chrysalis.
If you have this bar to the very left side, you will have no wait time and can instantly perform any action without waiting for the purchase to complete. If you want to make sure you do not accidentally spend any hard currency, slide the bar to the very right hand side and this will make the wait time longer - giving you more time to hit that cancel button.