What does the cryptic crossword clue "Set today on and off in classical colonnade (4)" mean?

The definition is "colonnade". The wordplay uses acrostic. first letters of "Set today on and" = STOA; definition: "colonnade" The answer is STOA.

Set today on and off in classical colonnade (4)

Daily Mail Cryptic #17518 | 27 Down | 2024-12-25 flower