The word anocheciese is the imperfect subjunctive form of anochecer in the first person singular. There are other translations for this conjugation.
See the full anochecer conjugation

anochecer

Me dijo que tenía que estar en el bosque hacia Segovia antes que anocheciese.
He told me he had to go to the woods along the road to Segovia... before nightfall.
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