Candidate auto duplicate check after offer approved and before offer extend state

Requirement from client that Candidate auto duplicate check should happen after offer approved and before offer extend state

Is this possible to add Initiate candidate duplicate check action in candidate selection process configuration like if we add action for offer approved state then duplicate check will trigger only at that state? Please suggest.

Generally it is suggests to add action at beginning of state only. Is there any impact if we add at Offer phase and offer approved state