Could you clarify the 4 sec auction intervall in the aFRR activation? Auctions every 4 sec, activation response requirement 5 min. How do these fit together?

The aFRR optimization (or auction) will run every 4 seconds. The ACE and the TSO demand can change at any time and the result of the optimization will reflect this.
The aFRR signal from a TSO to a BSP can also change every 4 seconds and the BSP should continously try to adapt to last setpoint.