visualvm history graph

You can do several things:

1. Go to tools>options and change 'Monitored Host' and/or 'Monitored Data' to something smaller than default 60 minutes. 60 minutes mean that the graph will remember data for last 60 minutes.
2. You can close other tabs ('Heap', 'Classes', 'Threads') to make a graph bigger.
3. You can use Tracer Framework to display your data. Tracer framework allows you to zoom-in zoom-out collected data.

[NOTE: This answer was last updated in January 2016 to reflect changes in JVisualVM.]

From VisualVM version 1.3 is Tracer framework accessibility in the plugins manager.

Tools->Plugins tab Available Plugins name Tracer-Monitor Probes

VisualVM v1.3 news