Either end of musician or poet's early period (4)
I believe the answer is:
morn
'poet's early period' is the definition.
(poetic term for morning)
'either end of musician' is the wordplay.
'either' becomes 'mor' (I can't explain this - if you can you should give a lot more credence to this answer).
'end of' suggests the final letters.
The last letter of 'musician' is 'n'.
'mor'+'n'='MORN'
'or' is the link.
(Other definitions for morn that I've seen before include "First part of day (poet.)" , "PM? No" , "Early part of day (poetic)" , "Day's first part(poetic)" .)