Fellow nurses worn-out continued at length (7,2)

I believe the answer is:
dragged on
'continued at length' is the definition.
'dragged on' can be an answer for 'continued' (I've seen this before). I'm not certain of the 'at length' bit.
'fellow nurses worn-out' is the wordplay.
'fellow' becomes 'don' (both can mean an academic).
'nurses' means one lot of letters goes inside another (nurse can mean to hold onto or harbour).
'worn out' becomes 'ragged' (I've seen this in another clue).
'don' going around 'ragged' is 'DRAGGED ON'.
Can you help me to learn more?
(Other definitions for dragged on that I've seen before include "failed to finish" , "continued tediously" .)
