Hi Mark, the full set of options for the JQuery Cycle Plugin are documented here as well as within the source code file \Web\Controls\SlidePanel.cs (if you have the source). mojoPortal implements most of the available options, so you can override the default behavior by adding "option=value" to the parameters of the portal: declaration. For example, to slow the andreasviklund-02-alt1 skin's image transition from the default 1 second (1000 ms) to 2 seconds, and the time between transitions from 4 seconds to 8 seconds:
<portal:SlidePanel id="spanel1" runat="server" CssClass="rotatecontainer" Speed=2000 TransitionInterval=8000>
Note that the value for time between transitions on the Cycle Plugin documentation is "timeout", but in mojoPortal it's TransitionInterval (I determined this by looking at the source code).
When I get a chance, I'll write a document that lists all of the available effects for SlidePanel, in terms of the variable names mojoPortal is using.