Time to celebrate Labour's help (6)

I believe the answer is:

mayday

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'help' is the definition.
(I've seen this before)

'time to celebrate labour's' is the wordplay.
'time' becomes 'may' (I've seen this before).
'to celebrate labour's' becomes 'day' (I can't explain this - if you can you should give a lot more credence to this answer).
'may'+'day'='MAYDAY'

Can you help me to learn more?

(Other definitions for mayday that I've seen before include "Request for help" , "Help urgently needed" , "call for help?" , "please help" , "International radio distress signal" .)

I've seen this clue in The Times.

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