To move the timeline, simply left-click and drag. When you release the timeline, it will move inertially.
While the timeline is moving, all the images from the cameras will be updated periodically, but this effect can slow down video playback on slow connections. You can deactivate this feature via the context menu, accessed with the right mouse button, by deselecting the Update instantly when moving option:
By deactivating this option, the camera images will only be updated to the timeline time when you release the mouse button, and the timeline will also no longer continue to move with inertia.