What do these access keys mean?

Hint 1 of 6:

Have you read the book on the age in the library?

Hint 2 of 6:

Then you probably know that the constellations play a bit role in this age.

Hint 3 of 6:

Go to the planetarium-type room next to the library and sit in the viewing
chair.

Hint 4 of 6:

Stars are best seen at night.

Hint 5 of 6:

So turn off the lights in the room and take a look at the sky.

Hint 6 of 6:

Specifically, look at the sky on the dates and times given in the codes.  I
don't think you have to be exact to the nearest minute, but you certainly
should try to view the sky to a time as close as possible.