So I'm trying to move keyframes in time by holding down the option/alt key (macbook) and dragging them to the left, but it just moves them off of the timeline and won't work.
How do I fix this?
Works fine for me in all versions of AE and all properties. I suspect that you are using improper technique.
Here's what you do. Select all keyframes for the properties you want to change. Hold down the alt/option key and click on the last keyframe on the right and drag to change the relative spacing between the keyframes. Click on any other keyframe or anywhere in the row and drag and all the keyframes move without changing the timing between them.
Just to be clear, if you have three keyframe set, one an 0, one at 10 frames and one at 20 frames and you select all keyframes, hold down the alt/option key and click and drag the keyframe at 20 frames to 40 frames you will now have a keyframe at 0, the second keyframe at 20 frames and the last keyframe at 40 frames but if you click anywhere other keyframe in the row and drag they will all move. If you have 50 keyframes in a property and you drat around the middle 10 keyframes, then you hold down the alt/option key and drag the last selected keyframe the first selected keyframe will stay put and the rest will move to retime the animation between the selected keyframes.