Mean to maintain time (7)
I believe the answer is:
average
'mean' is the definition.
(I know that mean can be written as average)
'maintain time' is the wordplay.
'maintain' becomes 'aver' (averring is a kind of maintaining).
'time' becomes 'age' (an age is a period of time).
'aver'+'age'='AVERAGE'
'to' is the link.
(Other definitions for average that I've seen before include "building society customer loses capital over time" , "Mean - norm" , "mean maybe" , "Mean - medium" , "It may be mean" .)