This is true for qRules in general - when we set the value of the command field, the data has to post back to the server in order for the code to execute.
Postback in browser forms does cause a delay.
I try to group my logic when possible (i.e. perhaps instead of caclucating a date diff when a field value changes, it could be done right before the form is submitted or when the XML is reloaded, etc) to prevent too many postbacks.
I'm not sure what can speed up the actual postback itself - I imagine some of it would have to do with the general configuration of the SharePoint server itself, and the speed of the network connection between the client & server, as well as the client machine config in terms of speed for re-rendering the form, but I'm just guessing on all of these.
Edited to add - you aren't being picky, you are doing your homework before your buy - that's why we have a trial, so keep the questions coming! :)