Bravely Second is a special command that will allow you to stop time and act first. This is done by using an SP Drink, which can be bought from Nintendo through micro-transaction or by letting the game in sleep mode for 8 hours. Aside from allowing you to perform an extra action, the damage and recovery limiters will be removed in this mode, allowing you to heal and deal damage over the 9999 ceiling. (999 for MP recovery)
Each action costs one SP, whether its as simple as using an item or using a conventional attack so make sure that you'll make that action count! Remember also that when you use abilities that consume BP in Bravely Second, SP will be consumed instead so be careful in what you select.