How to make a point where skeletons spawn only at night but leave in the day in minecraft?

Make a large enclosed room only 2 blocks high with a glass ceiling. Light up a HUGE area around the room but not the room itself. By large I mean 128 blocks in every direction. Then be at least 16 blocks away but less than 128 blocks away and just pass time while mobs start spawning. For any and all information about mob spawning watch the video below. You may want to watch it a few times to understand everything but its very thorough.