seule:我有英语题目问你!
every two days这种用法是有的，表示“每两天”，如：He goes to fitness center once every two days.而你的once two days是没有的，正确用法是上面这个例句的用法。或者two days' time这种用法也是有的，表示“两天时间”，如：He finished the outline of his essay in two days' time.