Insert a set of keyframes somewhere along the timeline after the last keyframes. I’ve used frame 70 in this example. The number of frames between the end of the fade-in sequence and the beginning of the fade-out will determine the length of time the text is displayed (stationary) on the screen. Select the frames in each layer from top to bottom at frame 70. Choose Insert > Keyframe. These keyframes will be where the fade-out animation begins.

Select all the keyframes within the first frame of the timeline and copy them (Edit > Copy Frames). Select the blank frames in all the layers at frame  90 using the Shift key with the mouse. Choose Edit > Paste Frames.