Since occasion can also be defined as an important time, event, celebration, I submitted: "I saw you at that occasion". DL marked it as incorrect. Comments?
What about "I saw you that time." Time and occasion can often be used interchangeably in English. One of the ways when I have to work out whether to use vez or tempo is to see if I can use the word occasion instead of time in the English sentence that I'm translating to Portuguese.