Can anyone definitively say whether the correct word would be 'or' or 'and' when using a phrase that provide that the later in time of two events should be chosen. The example would be: "Johnny was offered to choose the later of two dates, the day of that he won a foot race _____ the day that he found a watermellon."

So, should the blank space be replaced with "and" or "or"?

Please help to settle an argument and let me know which would be correct.

Thanks.