in once spare time中的once 指什么

英语翻译once upon a time,a man spent all his spare time in one o Time can you back once in?once once in a life time Once in love for a whole time. once upon a time in china Youare my once in a life time one time和once有什么区别? Once in spare time 前加什么 one time=once one time=once? once upon a time