These days may be more prevalent before the start of autumn (6,3)
I believe the answer is:
common era
'these days' is the definition.
(the current era)
'more prevalent before the start of autumn' is the wordplay.
'more prevalent' becomes 'commoner' (more common).
'before' means one lot of letters go next to another.
'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" .)