The first time you will speed up an action in the game (once you have finished the tutorial), you will get prompted if you want to keep showing Confirmation Popups

At anytime, you can enable or disable the confirmation to spend Bills in the game via Menu button (at bottom right corner of the screen) then on Settings button. 

Inside the Settings screen, set the "Confirmations" to ON or OFF and that's it!

Set it to ON to enable confirmations every time you tap on the Speed Up button:

Or set it to OFF to disable  confirmations every time you tap on the Speed Up button: