How To add blank part in video for 1 hour
I don't know if the AE encoder can signal duplicate frames (which would keep the size down). You may be better off using ffmpeg, a command-line tool.

Suppose your source video is 1280x720 at 24 fps, then you would run

ffmpeg -i source.mp4 -f lavfi -i "color=black:s=1280x720:r=24:d=3600" -filter_complex "[0][1]concat=n=2:v=1:a=0[v]" -map [v] -c:v libx264 output.mp4 




To combine with text overlay,

ffmpeg -i universal.mp4 -f lavfi -i "color=black:s=1280x720:r=24000/1001:d=20" -filter_complex "[0][1]concat=n=2:v=1:a=0[v];[v]drawtext=fontfile=FreeSerifB‌​old.ttf:text=\'Hello World\':fontcolor=white@1.0:fontsize=16:x=w-tw-10:y=10:box=1:boxcolor=black@0.5[vout]" -map [vout] -map 0:a -c:v libx264 -profile:v main -movflags +faststart output.mp4 2&gt;&amp;1