To add, edit or delete a time interval, please open the task that the interval is to be recorded for.
Once the task is open, please click on the small icon in the sidebar that says "Total time tracked" and a new menu will appear like in the image below.
When you reach this point you just have to select one of the time intervals, and you can already add, edit or delete any time intervals. Adding is done by clicking the "Add interval" button, deleting by clicking the "X" button that appears when you hover an interval, and editing, by clicking on the interval. See image below.
Note: If you don't have any time intervals for this task yet, please click on "Start Recording" and stop after a few seconds, then you can follow the steps above.