Antonyms for the phrase "occurred simultaneously" include "sequential," "consecutive," "successive," "gradual," "delayed," "sporadic," and "intermittent." These words imply an action that occurs in a particular order, rather than all at once. Sequential means occurring in a specific order, while consecutive refers to events that follow one another without interruption. Successive denotes events that occur one after another, while gradual means a slow, steady progression. Delayed and sporadic suggest an action that is late or infrequent, respectively. Intermittent indicates a stop-and-start rhythm, with periods of activity alternating with periods of rest. Overall, these antonyms highlight the importance of timing and progression in the occurrence of events.