I dont really think that they updated the mcu.
I think it is more like changing the drivers or the settings of the drivers in android.
The MCU tells the SNT-driver that an event of ACC-off occured. The driver reacts on that event.
I think that they changed something in their library/driver/setting files in Android so that the system reacts differently, in our case exactly 1min after turning off ACC.
As I've saw, they also write some xml Files in android like:
/mnt/sdcard/update/system/third_party/cusp/sntron/FactorySetting.xml
/mnt/sdcard/update/system/sntron/DeviceSetting.xml
May be the shutdown time is somewhere saved there and read by SNT-IVI.apk, SNT-SYSTEM.apk or data/property/persist.sntron.factory.MCU.