when的意思:1,什么时候,用于提问,如:When did you last see him?
2,在那时,用于时间的表达方式之后,如：Sunday is the only day shen I can relax.
3,在……之后,如：Call me when you have finshed.
4,一……就……,如：He had just drifted lff to sleep when the phone rang.
5,当……时候,如：When I was young,I had a lovely cat.
until的意思：到……时,到……为止,如：Let us wait until the rain stops.