An indefinite number jump off the top tee mid-morning (7)
I believe the answer is:
umpteen
'an indefinite number' is the definition.
(I've seen this before)
'top tee mid-morning' is the wordplay.
'top' becomes 'ump' (I can't explain this - if you can you should give a lot more credence to this answer).
'mid' says to take the centre (mid- can mean the middle of something).
The centre of 'morning' is 'n'.
'ump'+'tee'+'n'='UMPTEEN'
'jump off the' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for umpteen that I've seen before include "Lots of things on pet menu" , "Indefinitely many" , "An uncountable number" , "Uncountably many" , "Pet menu for a great many" .)