That's not what IEX does. IEX is, to fit within your example merely exchange A. It can't control whether you delay your order to B or C or not. What A does do

That's not what IEX does. IEX is, to fit within your example merely exchange A. It can't control whether you delay your order to B or C or not. What A does do is delay the output. When it receives an order it doesn't immediately broadcast that information back out, it waits some small (but relevant) period of time.