I don't see an option for this in properties.
Once it's on the timeline, place your mouse at the end and drag to the required duration. The default is 5 seconds. You can change the default duration for all annotations if required - go to Edit>Preferences>Timing and input the required duration.
I hope this helps,
Hello, if I understand your question correctly, you are wanting to set the duration? With your annotation callout at the preferred starting place, simply drag to extend it on the timeline track. You may right click on the item and select Duration if you prefer to enter the time: