diary-remind-message is a variable defined in `diary-lib.el'.
Its value is shown below.

Pseudo-pattern giving form of reminder messages in the fancy diary display.

Used by the function `diary-remind', a pseudo-pattern is a list of
expressions that can involve the keywords `days' (a number), `date'
(a list of month, day, year), and `diary-entry' (a string).

You can customize this variable.


("Reminder: Only " (if (zerop (% days 7)) (format "%d week%s" (/ days 7) (if (= 7 days) "" "s")) (format "%d day%s" days (if (= 1 days) "" "s"))) " until " diary-entry)