Back when I used to work in Flash, if you realized you needed something to take longer, you could add frames and everything in the timeline would shift.
So say you had an effect at 60 frames into the timeline. Let's say that effect lasts 30 frames, followed by another effect that starts 90 frames in. You realize you want the first effect to last 40 frames instead of 30.
In Flash, you could put your cursor in the timeline at frame 60, add 10 frames and everything would shift (so now the second effect starts 100 frames in instead of 90).
Is there a way to do something similar in After Effects? It seems like once you set things up, it's very cumbersome to change something in the middle. I find myself selecting multiple layers and keyframes and manually dragging them. Maybe a keyboard combination that moves selected layers frame(s) at a time?