Crossword Genius

Muses say hr/3600 is briefer than brief (7)

Ross

I believe the answer is:

sisters

I'm a little stuck... Click here to teach me more about this clue!

'muses' is the definition.
The answer and definition can be both people as well as being plural nouns.
Maybe you can see a link between them that I don't see?

'hr3600 is briefer than brief' is the wordplay.
I cannot really see how this works, but
'is' is within the answer.
This explanation may well be incorrect...

'say' acts as a link.

Can you help me to learn more?

(Other definitions for sisters that I've seen before include "Nuns - nurses - siblings" , "Resists for relatives" , "Female siblings" , "Resists (anag)" , "Relatives in hospital?" .)

I've seen this clue in The Telegraph.
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