If you want to delete a worktime in the Day view you can easily do this as followed.

Click on the worktime you want to delete. You hold it and you will see that the trash can appears. You drag the work time to the red area of the trash can.

In the weekplanner, you can do this exactly the same way or via the 3 dots in the corresponding work time.

You will see that you can then select "remove" .