Sometimes fermentation can finish in as little as a few days which is more likely when at higher temperatures.
Do not exceed recommended temperatures as fast fermented Ginger Beer will come at the expense of taste, or you could kill the yeast altogether.
If you are unsure if it has completed fermentation, once you notice the airlock has stopped bubbling take a gravity reading and then two days later take another reading.
If the reading is the same, then it has completed fermentation. If it has changed, let it ferment for a few more days and wait until the readings are consistent for at least 2 days.