What does the cryptic crossword clue "Time for pranks agitates fairly old OAPs (5,5,3)" mean?

The wordplay uses an anagram. anagram of FAIRLY + OLD + OAPS = APRILFOOLSDAY The answer is APRILFOOLSDAY.

Time for pranks agitates fairly old OAPs (5,5,3)

Daily Mail Cryptic #16339 | 15 Across | 2020-06-17 flower