Enigma: a Question from WW2 I have seen in the Imitation Game that the Germans reset the Enigma at midnight sharp, and then they start messaging by sending the weather report in the morning.

But the device made by Alan Turing, the Christopher, sometimes only took a few minutes to decode Enigma.

How did the German receiver know the settings of the machine? I thought that they may be sending the next day's setting at midnight, but if they were compromised once, the enemy would know all the next day's settings too. 

So, how did they do it?
The simple answer is also part of one weakness with all encryptions that use symmetric key, AKA pre-shared key. Key sheets that lasted 31 days where generated and sent out by courier or so. The weakness is ofcourse that if the enemies get their hands on it then they can read all the messages that used that key. 
And yes - sometimes the allied did get their hands on a key sheet and then they had the keys for one network for up to a month.