Lawyer's right to welcome one extended rest (3-2)
I believe the answer is:
lie-in
'one extended rest' is the definition.
(I've seen this before)
'lawyer's right to welcome' is the wordplay.
'lawyer's' becomes 'i' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'right' becomes 'lien' (legal right).
'to welcome' means one lot of letters goes inside another (inserted letters are welcomed in).
'i' put within 'lien' is 'LIE-IN'.
Can you help me to learn more?
(Other definitions for lie-in that I've seen before include "time spent with crossword, perhaps" , "Extra snoozing" , "Extended time in bed in the morning" , "Extra time in bed" , "Extended bedtime!" .)