there have been some opinions that old, pre-1.6 graph control system had better time period control in some scenarios.
here's an idea to mix the functionality :

if a user clicks < > buttons or cliks and drags arrows on the scrollbar, do whatever is done now. if, however, user clicks and holds, provide a dropdown menu which would list options like change/increase/decrease displayed period by some time (hour, 2 hours, 4 hours, 8 hours, 12 hours, 1 day, 2 days, week, month...).

clicking and holding on < and > buttons would provide entries for moving the period;
clicking and holding on the outer arrow of the scrollbar would provide options to increase the period;
clicking and holding on the inner arrow (once that is implemented) would provide options to decrease period