I don't believe it! A schedule! (4)

I believe the answer is:

rota

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

'i don't believe it a' is the wordplay.
'i don't believe it' becomes 'rot' (I can't explain this - if you can you should give a lot more credence to this answer).
'rot'+'a'='ROTA'

Can you help me to learn more?

(Other definitions for rota that I've seen before include "Repetitious canon" , "Work roster" , "List of people to do job in turns" , "Roll call or roster" , "Duty roster" .)

I've seen this clue in the Evening Standard.

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