This function is used to get the time it takes for a Drag Start Gesture event to be triggered by a touch or click. This time will also affect how the Tap Event is triggered as a touch/click and release before this time is up will be considered a Tap. The time is measured in seconds and has a default value of 0.16.
Real (time in seconds)
if gesture_get_drag_time() != 0.16
The above code checks to see if the drag time for gestures is set to 0.16 seconds and if it is not it sets it to that value.