All phases of the Stirling cycle take place every half turn of the engine.
It takes two full engine revolutions to make a Stirling cycle.
Each volume of gas is transferred from chamber to chamber.
The Stirling engine is in engine phase every half turn.
The compression phase is a true isothermal compression phase.
The engine phase is a true isothermal expansion phase.
The temperature rise phase is a true isochoric phase except that the gas is preheated via a heat exchanger and not a regenerator.
The cooling phase is a true isochoric phase except that heat is recovered via the exchanger and not a regenerator.
the website allows a better understanding, but it is considered as a commercial site by this post
I regret not being able to give more explanation. normandajc
If this image can help to understand. These steps take place simultaneously during half a revolution of the engine.