Ungenerous period for interval (8)
I believe the answer is:
meantime
'interval' is the definition.
(meantime is a kind of interval)
'ungenerous period' is the wordplay.
'ungenerous' becomes 'mean' ('mean' can be similar in meaning to 'ungenerous').
'period' becomes 'time' (time is a kind of period).
'mean'+'time'='MEANTIME'
'for' is the link.
(Other definitions for meantime that I've seen before include "Intervening period" , "For the moment" , "interim?" , "interval" .)