To delete a timer start event or timer end event you’ve set, right-click the event mark in the event area and then select [Delete Events] on the context menu that is displayed.

You can also delete a timer start or timer end event on the Events panel which opens by selecting [View] menu >> [Event]. After selecting the timer start or timer end event (execution-related or access-related) displayed in the detailed information on the timer result in the Events panel, click ( ) button on the toolbar to delete it (see "2.17.5 Deleting events").