Stay, due to change in part of week (7)
I believe the answer is:
tuesday
'part of week' is the definition.
(I know that Tuesday is part of the week)
'stay due to change' is the wordplay.
'to change' indicates anagramming the letters.
'stay'+'due'='staydue'
'staydue' anagrammed gives 'TUESDAY'.
'in' is the link.
(Other definitions for tuesday that I've seen before include "Day of the week" , "Shrove ____" , "Sea duty (anag)" , "24 hour" , "forty eight hours before Chesterton's man" .)