Waste time when there's dirt all over (4,5)
I believe the answer is:
once again
'over' is the definition.
(I've seen this in another clue)
'waste time when there's dirt all' is the wordplay.
I cannot quite see how this works, but
'time' could be 'again' (I have seen 'Next time' mean 'again' so perhaps 'time' could also mean 'again') and 'again' is found in the answer.
'when' could be 'once' (synonyms) and 'once' is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for once again that I've seen is " encore".)