Delay
Here are the delays for Transform and Repeater.
Repeater Delay
This is probably the hardest setting to fully comprehend. It allows for an animation delay for the parameters in the "Repeater" group.
Transform Delay
This setting allows for an animation delay for the Transform parameters on the original layer. This is useful for creating time-rippling animations, where first the original layer moves (or rotates etc) and then the instances follow after a certain time. Here is an example: