Means to declare time on Sunday (8)
I believe the answer is:
averages
'means' is the definition.
(mean is a type of average)
'declare time on sunday' is the wordplay.
'declare' becomes 'aver' (averring is a kind of declaring).
'time' becomes 'age' (an age is a period of time).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'sunday' becomes 's'.
'aver'+'age'+'s'='AVERAGES'
'to' acts as a link.
(Other definitions for averages that I've seen before include "Statistical norms" , "Save rage (anag.)" , "Evens out to" , "Means" , "that are of great concern to cricketers" .)