Strictly speaking, temporal logic does not so much 'depart' from FOL. It's a modality, hence like other modal logics it can be viewed as a restriction of full

Strictly speaking, temporal logic does not so much 'depart' from FOL. It's a modality, hence like other modal logics it can be viewed as a restriction of full FOL (where the domain of discourse can be seen as some notion of 'possible worlds') with some desirable properties such as better computational tractability.