Template:KeyframesInTheTimebar
From Synfig Studio :: Documentation
You can adjust the Time of a keyframe by a normal drag and drop. To adjust it's Length, hold Alt key when releasing the mouse button.
During a keyframe drag and drop operation a tooltip indicator will be displayed with some time informations.
Right click over a keyframe or in upper part of the "Timebar" open the keyframe contextual menu giving access to the keyframes actions.