Do you mean you are waiting for several tens of seconds between the moment you start the workflow and the moment workflow presentation wizard pops up? Usually this means your workflow presentation has a lot of OGNL expressions/scripting actions attached to input fields, and evaluation of this logic takes a very long time.
In the current vRO workflow designer, there is no way to switch this logic to be executed on the background. You can play with some of the options exposed under Tools > User Preferences (eg. Validate a workflow before running it), but I doubt it will improve the presentation startup time a lot. What you can do is to revisit your presentation logic and try to optimize it.
