There are several synonyms for the phrase 'in due.' One such synonym is 'in time,' which refers to something happening at the appropriate or expected moment. 'Timely' is another synonym for 'in due,' indicating that an event or task has been completed promptly or punctually. 'Suitable' is yet another synonym, signifying that something is appropriate or fitting for a particular situation. Another synonym for 'in due' is 'fitting,' suggesting that something is right or proper given the circumstances or context. Additionally, 'just' and 'proper' can also be synonyms for 'in due,' indicating that something is morally or ethically righteous and appropriate.