A method implemented by a computational assistant (122, 122A, 122B) executing at one or more processors, the method comprising: receiving a representation of an utterance spoken at a computing device; identifying, based on the utterance, a task to be performed by the computational assistant (122, 122A, 122B); determining that complete performance of the task involves the computational assistant (122, 122A, 122B) performing one or more sub-tasks, wherein at least one of the sub-tasks involves the computational assistant (122, 122A, 122B) interacting with a person or computing system other than a user of the computing device; determining that complete performance of the task will take more than the threshold amount of time in response to determining that at least one of the one or more sub-tasks is marked in a task data store as not being eligible for immediate performance, wherein the sub-task of interacting with the person or computing system other than the user of the computing device is not eligible for immediate performance; responsive to determining, by the computational assistant (122, 122A, 122B), that complete performance of the task will take more than a threshold amount of time, outputting, for playback by one or more speakers operably connected to the computing device, synthesized voice data that informs the user of the computing device that complete performance of the task will not be immediate; and performing, by the computational assistant (122, 122A, 122B), the task, wherein during performance of the task: receiving, by the computational assistant (122, 122A, 122B) and before performance of the task is complete, a representation of an additional utterance spoken at the computing device, the additional utterance comprising a request to modify one or more parameters of the task; and causing the computational assistant (122, 122A, 122B) to complete the performance of the task with the modified one or more parameters. receiving a representation of an utterance spoken at a computing device; identifying, based on the utterance, a task to be performed by the computational assistant (122, 122A, 122B); determining that complete performance of the task involves the computational assistant (122, 122A, 122B) performing one or more sub-tasks, wherein at least one of the sub-tasks involves the computational assistant (122, 122A, 122B) interacting with a person or computing system other than a user of the computing device; determining that complete performance of the task will take more than the threshold amount of time in response to determining that at least one of the one or more sub-tasks is marked in a task data store as not being eligible for immediate performance, wherein the sub-task of interacting with the person or computing system other than the user of the computing device is not eligible for immediate performance; responsive to determining, by the computational assistant (122, 122A, 122B), that complete performance of the task will take more than a threshold amount of time, outputting, for playback by one or more speakers operably connected to the computing device, synthesized voice data that informs the user of the computing device that complete performance of the task will not be immediate; and performing, by the computational assistant (122, 122A, 122B), the task, wherein during performance of the task: receiving, by the computational assistant (122, 122A, 122B) and before performance of the task is complete, a representation of an additional utterance spoken at the computing device, the additional utterance comprising a request to modify one or more parameters of the task; and causing the computational assistant (122, 122A, 122B) to complete the performance of the task with the modified one or more parameters. receiving, by the computational assistant (122, 122A, 122B) and before performance of the task is complete, a representation of an additional utterance spoken at the computing device, the additional utterance comprising a request to modify one or more parameters of the task; and causing the computational assistant (122, 122A, 122B) to complete the performance of the task with the modified one or more parameters.