Once more it was the middle of the night, the moon out in full but shrouded by dark misty clouds. The bells had not rang for some time, for a long time. The owl stood in wait as a young girl came out to pray. By an old oak tree, she fell to her knees. then she heard a voice, one that lured her towards it, against her own will.. There stood a woman looking young in age ringlets flowing down her back. The woman turned her eyes blue but something was wrong, with her eyes. They looked as though they were that of snakes.

"My name is Christabel, I was brought here against my will, please help me"

and so it continued the old oak tree collecting the souls that were lost.

"'Tis the middle of night by the castle clock,"

"The thin gray cloud is spread on high,"

"The moon is behind, and at the full; "

"The night is chill, the cloud is gray:"

"Is it the wind that moaneth bleak?"

Specifically what is the significance of it being "middle of the night"?

the middle of the night is the height of a womens power ("midnight represents the zenith of the feminine principle.")

How does this complex symbolism add to the ambiguity of both Christabel and Geraldine?

" I saw a bright green snake

Coiled around its wings and neck." ---> The devil disguised itself as a snake in the Garden of eden to trick Eve, Geraldine disguised herself as well and trick Christabel into letting her into her home in order to take her place

Evidence:

"'Tis the middle of night by the castle clock,

And the owls have awakened the crowing cock"

Though thou her guardian spirit be,

Off, woman, off! 'tis given to me.'"

Geraldine is talking to the dead, and casting off Christabel last line of defense (taking youth from her mother)

2. "Again the wild-flower wine she drank:

   Her fair large eyes 'gan glitter bright,

   And from the floor whereon she sank,

   The lofty lady stood upright:

   She was most beautiful to see,

   Like a lady of a far countrèe."---> feeding on something that is important to Christabel

3. "Behold! her bosom and half her side—

   A sight to dream of, not to tell!

   O shield her! shield sweet Christabel!"---> taking away her innocence

   
   

And eyes the maid and seeks delay;

Then suddenly, as one defied,

Collects herself in scorn and pride," ---> she delayed, Geraldine hesitated before tainting Christabel proving that she does have some good in her but she still "collects herself in scorn and pride" aka collects herself in sin giving into her evil nature

in this case I don't believe that Geraldine is a symbol of literal death but death of innocence and a life that once was. Geraldine taeks both of these thing from Christabel.