Youth leader said Esther spent a significant time here in the old days (10)
I believe the answer is:
yesteryear
'days' is the definition.
(I have seen 'Nostalgic days' mean 'yesteryear' so perhaps 'days' could also mean 'yesteryear')
'youth leader said esther spent a significant time here in the old' is the wordplay.
I cannot quite see how this works, but
'youth' could be 'y' and 'y' is located in the answer.
'leader' could be 'e' (I've seen this in other clues) and 'e' is found in the answer.
'said' could be 't' (I've seen this in other clues) and 't' is present in the answer.
'a' is found in the answer.
'the old' could be 'ye' (resembles a historical spelling of 'the') and 'ye' is found in the answer.
The remaining letters 'serr' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for yesteryear that I've seen before include "Former times" , "Days gone by" , "nostalgic time, perhaps" , "Time disappeared" , "Days of old (poet.)" .)