Sat thus starting off sitcom? (7)
I believe the answer is:
friends
This could be a double definition.
'sat thus starting' is the first definition.
(when Friday ends, Saturday starts)
'off sitcom?' is the second definition.
'friends' can be an answer for 'sitcom?' (US sitcom). I am not sure about the 'off' bit.
(Other definitions for friends that I've seen before include "playmates!" , "Pals, comrades" , "Buddies" , "American sitcom" , "Chums" .)