Based on the OP's diagram ( and assuming it's an accurate representation) I don't see the need to delay these side fills. People on the sides are closer to the speakers but not really that much closer to the fills than the mains. Unless reality is different from pic. Unlike front fills, don't most of us place our side fills right beside our mains?
Anyone who can hear both , for all practical purposes, will be equal distant from both, within a foot or two. No one is going to hear that.
Sent from my iPad using Tapatalk