What boy working with monk after hours produces? (8)

'hours produces?' is the definition.
I know nothing about this answer so I cannot judge whether this works.

'what boy working with monk' is the wordplay.
'what' becomes 'h' (I can't explain this - if you can you should believe this answer much more).
'working with' indicates an anagram (working with the letters).
'boy' with its letters anagrammed with 'monk' makes 'ymnbook'.
'h'+'ymnbook'='HYMNBOOK'

'after' is the link.

Can you help me to learn more?