Left-clicking and dragging moves a single marker to a new location on the timeline.
It is possible to move multiple markers by the same distance. Left-clicking each discreet marker, or Left-clicking the first and last markers of a range of markers selects them, then dragging one to a new location will move all selected markers together.
The markers are bounded by the zero point on the timeline. In other words, the first marker in the selection cannot move to the left of zero on the timeline.
Both ends of a range marker
By left-dragging either end of the range marker, the other end will move by the same distance.