When King Haakon and Prince Olav hear the news of the German surrender, it is light outside. In reality, the surrender instrument was signed at 9:20 p.m. in Germany, which would make it 8:20 p.m. in the UK, where the Norwegian king and crown prince are living in exile. It would be dark already.
The mistake is especially glaring when the princess and her children learn of the news in the US. It is daytime there, and the light looks almost identical to the light in the UK, even though it's much later in England.