Conflicting notices about upcoming period (2,4)
I believe the answer is:
at odds
'conflicting' is the definition.
(synonyms)
'notices about upcoming period' is the wordplay.
'notices' becomes 'ads' (advertisements).
'about' indicates putting letters inside.
'upcoming' says the letters should be written in reverse (in a down clue coming up is backwards).
'period' becomes 'dot' (as in a full stop).
'dot' backwards is 'tod'.
'ads' enclosing 'tod' is 'AT ODDS'.
(Other definitions for at odds that I've seen before include "Not in agreement" , "At variance (with)" , "In disagreement or conflict - like bookies?" , "Quarrelling" , "In disagreement or dispute" .)