I was told that after you cut in a room that you had to roll the walls before the cut in paint drys, is that true?
Normally you should begin rolling as soon as possible to avoid picture framing, a visible difference between the rolled and brushed paint. A true answer depends on the paint (manufacture and quality), sheen and color. The color can really affect how a paint works. Dark or "true" colors will be affected more that light off white colors. A flat sheen will be affected most as it dies faster.