That depends on the particular service. There is no one answer for all services. Some stop immediately, and will not let you sign up again and get the remainder of the previous trial. Others simply stop it at the time of the free trial.
Keep in mind that the purpose of a free trial is actually to determine if you want to use the service. If you decided you don't, and cancel, then an immediate cancelation would not be an issue. At least, that's the viewpoint of those offering the trial (the actual service). Others will leave it hoping you'll change your mind and stay.
DBDukes Roku Community Streaming Expert Note: I am not a Roku employee.
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