Assuming the board is inserted between a PC and a target device, I must say the hardware solution for the function, monitor/intercept/delay USB transfer, is overkill. Adding only thirty to forty lines code to SnoopyPro, you can get a prototype of the function.

USB applications are a combination of firmware (and device), device driver and host application. If you have the Axelson's book, you'll find that he spent one third to protocol, another one third to device and firmware, and the last one third to device driver and host application. Even if you are a hardware or firmware designer, you should know at least what the PC can do. Then you can find the best solution.

When I design an USB application, I make the firmware and the device driver as simple as possible. I assign most of functions to the host application. PC has much more resources and execution speed than MCU.

Tsuneo