Hi alexban,
my understanding with the B737NG CFM56-7 engine is that,
when the OAT is -35 to -40 degC, the engine is to be held at idle for two minutes.
Then an overall statement that says that anytime the engine oil pressure is outside the normal operatiung range, stay at idle.
Then, after landing, the normal cooldown time should be three minutes, but if its absolutely needed, one will suffice.
After 3 or more hours cold soak at -40 or less, do not start or motor until maintenance has done their procedure with the starter.
hope this helps,
FD