Why couldn't harry see the thestrals from the beginning?

Which two parts of this excerpt from mary shelley’s frankenstein reveals information about the setting? (it was on a dreary night of november that i beheld the accomplishment of my toils.) with an anxiety that almost amounted to agony, (i collected the instruments of life around me, that i might infuse a spark of being into the lifeless thing that lay at my feet. it was already one in the morning; the rain pattered dismally against the panes, and my candle was nearly burnt out) when, by the glimmer of the half-extinguished light, i saw the dull yellow eye of the creature open; it breathed hard, and a convulsive motion agitated its limbs. (how can i describe my emotions at this catastrophe), or how delineate the wretch whom with such infinite pains and care i had endeavored to form? his limbs were in proportion, and i had selected his features as beautiful. beautiful! great god! (his yellow skin scarcely covered the work of muscles and arteries beneath; his hair was of a lustrous black, and flowing; his teeth of a pearly whiteness; ) but these luxuriances only formed a more horrid contrast with his watery eyes, that seemed almost of the same color as the dun-white sockets in which they were set, his shriveled complexion and straight black lips.