Another example:
Today is 20 January 1943. U-Boat coordinates are 18°40'N 72°59'W. GMT is 18:01:30 and local time is 13:01:30 (GMT -5).
The sun is under horizon ¯\_(ツ)_/¯
I can observe Moon at true azimuth 73°58' and altitude 10°34'
Now go to Stellarium to the same place and the same time. But to get the same position of celestial bodies it needs to take GMT +5 time.
So in real life we have this celestial bodies position at 23:01:30 GMT and in SH at 18:01:30 GMT. It should not be like that.
It looks like Real Navigation uses GMT time as a local time.
[EDIT] It happens at initial loading. If you start mission or campaign at GMT +1 time zone you should ALWAYS subtract 1 hour from GMT time. Or if you starting point at GMT -5 time zone you should always add 5 hours to GMT. So so-called "GMT" time is local time at your starting point. I checked it with transatlantic trip.