Sliding keyframes in batches up & down timeline

When animating complicated scenes with parallel actions in different parts of the set, I found myself needing to set the animation right linearly, as I moved on, in every part of the scene, because going back for adjustments in the timing was very difficult. If I miscalculated the duration of the parallel action and needed to slide down the timeline a complicated animation with multiple characters, I found I had to slide one by one each keyframe from each character. I would stick to the screen a strip of paper where I could mark with a pencil the relative positions of the keyframes, so that I could quickly arrange them again at their new placement on the timeline, but there's got to be a better way of doing this. If we could only select batches of keyframes and slide them together up and down the timeline, that would really help make corrections, even if we had to do it one character at a time. If we could do it for multiple characters that would be even more helpful.