You should treasure every encounter, for it will never recur.

vicissitudes, the way that the world or a person prospers one day and declines the next

dotting the i's and crossing the t's

successive series of questions and responses

a lucky day, auspicious day

(rare) one's birthday

Saturday

(rare) a birthday

a red sun, a bright sun, or the summer sun / a day in the traditional Japanese six-day week which is unlucky except for at noon

the last day of the year, New Year's Eve