The most common and most likely answer to this crossword clue is the 5 plus 2 letter word SLEEP IN
I've seen this crossword clue in The Times
S
L
E
E
P
I
N
Buddy explains!
The straight part
We know that "to have an extended rest" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case to have an extended rest = sleep in.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SLEEP IN mean?
SLEEP IN noun- An instance of sleeping in, sleeping late, sleeping until one feels fully refreshed rather than rising at a prespecified time.