Compact Block Relay (BIP-152) introduced an efficient way to relay the block when there is a good member synchronization between nodes.
The figure means that the block can be delivered before the receiving node processes.
Do you want to know what the situation is in Bitcoin Core?
I think this is safe.
- All block reception (important path)
- POW and MERKLE ROOT FARST (Critical Path) Check
- Block relay (can be done by a thread other than a critical path)
- Check it completely and connect the block (important path)
- New tip mining starts (important paths)
What is the delay between receiving and sending?
Socket loops have a 50ms delay and POW and MERKLE ROOT can be ignored, so when the block is spread, the internal delay of the node should not be added or more. What happens if you wait for the entire verification, or is the propagation blocked?