After stopping the Mercedes E-Class engine (W211), its residual heat is sufficient to heat the passenger compartment for 30 to 60 minutes, and the exact time is largely dependent on the already installed temperature in the passenger compartment. The fan is working at a low stage, regardless of the air supply.
When the "Engine residual heat" function is activated at high temperatures, only the middle stage ventilation system is automatically activated. This function is enabled as follows: You must install the key in the ignition locking system at position 0, press the REST button (with an indication on the display).
The engine's residual heat shall be switched off automatically after 30 minutes or if the ignition is on or the battery voltage has fallen.