it wasn't until he turned 50 age翻译

Question

it wasn't until dusk that he realized that it was too late to return home
为什么用wasn't until,用it was until dusk.翻译也通啊,直到天黑吗

Answer 1

until是“直到”
not until是“直到……才”
就是说,如果用until,这个句子的意思是,他在天黑前一直都知道这件事.当然要表达这个意思,一般是不会这么说的.
not until,意思是,他在天黑后才知道这件事