On second thoughts, rearrange odd Orff and put middle at the end (13)

'the end' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'on second thoughts rearrange odd orff and put middle' is the wordplay.
I cannot quite understand how this works, but
'and' could be 'n' (common abbreviation for 'and') and 'n' is found within the answer.
'middle' could be 'heart' (synonyms) and 'heart' is found in the answer.
'second thoughts' could be 'h' (2nd letter of 'thoughts') and 'h' is found in the answer.
This may be the basis of the clue (or it may be nonsense).

'at' is the link.

Can you help me to learn more?