These days may be more frequent before the start of autumn (6,3)
I believe the answer is:
common era
'these days' is the definition.
(I've seen this before)
'more frequent before the start of autumn' is the wordplay.
'more frequent' becomes 'commoner'.
'before' is a charade indicator (letters next to each other).
'the start of' indicates taking the first letters.
The first letter of 'autumn' is 'a'.
'commoner'+'a'='COMMON ERA'
'may be' is the link.
(Other definitions for common era that I've seen before include "In Christian times" , "this time" , "these days" .)