The MiniMap tool allows you to change the size of the timeline. Reduce the size of the MiniMap to zoom in on the timeline; increase the size of the MiniMap to zoom out on the timeline.

You can drag and drop the borders of the MiniMap tool to change the timeline scope, or zoom in and out with your mouse wheel while hovering over the timeline or MiniMap.

See the GIFs below for a demonstration on how the MiniMap tool affects the scope of the timeline: