in an hour's time/in an hour

$\$frac{\text{In an hour's time}}{\text{A}} I had done the work with my satisfaction, I got my hat in the hall and slipped

out unnoticed. (全国研考)

(在一小时内我就把工作满意地干完了,然后,我在大厅内拿起帽子,谁也没有觉察到,我就溜走了。)

答案为 B(应将 with 改为 to)。但我认为 in an hour's time 用在这里是错误的。