Thanks for your feedback. Now I understand the use case and it is indeed quite useful.
I have coded up support for user defined Trainer Lag compensation. (Up to 10secs). Hence in your case, putting it at 4secs, the app will send the Next Power Target (Slope% or Watt) per the structured workout to the smart trainer 4 seconds earlier so it will sync to the Next Lap Start.
Will send it to the Apple App Store in the next release cycle.
Tx.