This free script allows you to easily navigate in timeline. You can change the active time segment by dragging the slider, or zooming with your mouse wheel.
Bug report: email@example.com
1.6.1 (2013. Apr 7.) Error in new scene fixed, callback event error fixed, zoom to selected keyframes works with biped objects.
1.6 (2013. Mar 19.) Available to Zoom to selected keyframes.