What I understand is it is a permanent stretch of the vessel wall. Is this true or does it mean something else?
First let's consider what compliance means:
C = compliance
ΔV = change in volume
ΔP = change in pressure
Delayed compliance The response of a blood vessel to a sudden change in pressure. When the volume and so the pressure highers in the blood vessel the vascualar wall will stretch. As the wall of the vessel stretches the pressure inside the vessel will fall. So an increase of compliance is the result(look at the formula ΔV will get higher because the wall stretching will make the vessel larger at so the volume bigger and the pressure less). this change in compliance is what they call delayed compliance.
I don't really think you can speak about permanent because it's a dynamic process.