在day off前是加介词ON 还是介词 IN?

问题描述:

在day off前是加介词ON 还是介词 IN?

on
day off表示“休息日,假日”,是具体某一天,介词用on.比如:
On their day off,they visited the aquarium.在休息日里,他们参观了水族馆.