Is to set off round about six – flying (6)
I believe the answer is:
exists
'is to set off round about six flying' is the definition.
I can't judge whether this definition defines the answer.
'is to set off round about six flying' is the wordplay.
'to' says to put letters next to each other (I've seen this in other clues).
'off' indicates anagramming the letters.
'round' means one lot of letters goes inside another.
'about six flying' becomes 'x' (I can't justify this - if you can you should give a lot more credence to this answer).
'is' put after 'set' is 'setis'.
'setis' with letters rearranged gives 'eists'.
'eists' going around 'x' is 'EXISTS'.
Can you help me to learn more?
(Other definitions for exists that I've seen before include "Subsists" , "Has being, is actual" , "Is present in the universe" , "Has objective reality" , "Has life" .)