So far, we didn’t have the option to create recurrence/repeated tasks in period of time in Panner Plans. With the new addition of the Recurrence field it’s possible to create that kind of Tasks in Planner Plan by simply choosing the recurrence period.
In order to visualize the recurrence of a given Tasks, we need to access the Schedule view. In the other Planner Plan views we are not going to see the recurrence, only the task has been defined as recurrent.
Finally, I recommend you to review the official announcement of this feature in the Planner blog so you can review all the details of this functionality as well as some FAQs.
Reference: Introducing recurring tasks and grid features in Planner – Microsoft Community Hub