Stretch or Change Timing in After Effects
The solution will be found in the Timeline. Scroll through the items in the timeline until you find the track for the text object you want to change. The duration of the text on screen is defined by starting and ending keyframes on the object's track.  

Moving the last keyframe on the object's timeline will extend the duration of an object, so clicking and dragging the last keyframe for the text will extend how long it is on screen.