"-interval=0" command line option is accepted. In this case jconsole doesn't update content at all. It seems that such functionality is useless for an ordinary user.
Also, negative numbers are accepted and the following exception is printed:

Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: Non-positive period.
        at java.util.Timer.schedule(Timer.java:221)
        at sun.tools.jconsole.VMPanel.startUpdateTimer(VMPanel.java:442)
        at sun.tools.jconsole.VMPanel.propertyChange(VMPanel.java:321)
        at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:339)
        at javax.swing.event.SwingPropertyChangeSupport.firePropertyChange(SwingPropertyChangeSupport.java:75)
        at javax.swing.event.SwingPropertyChangeSupport$1.run(SwingPropertyChangeSupport.java:80)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)