In the QV management console, you can have a continuous reload of your application. If you connect the application with the updated source, this should be doable. However, I guess once you open the application, the update process for that open application would possibly stop. That's to check.
Real time is probably not the right word for it. In the best of cases you can maybe get close to "near real-time". Using QVD's or Direct Discovery is never real time.
Direct Discovery could be a good solution but it depends on whether you can live with the restrictions it puts on your analysis. For instance you can't use Set Expressions (popularly referred to as Set Analysis) with a DD source.
QVD's are much less close to anything real-time. But you could depending on the way and the volume you extract get it down to a few minutes or even minute level of refresh. Usually you would limit it to every hour or half-hour. An often recurring reload partial or full might disrupt the normal work-flow for your users if it is not crafted carefully.
The SET DirectCacheSeconds=XX will NOT automatically refresh the client at given intervals. You have to do additional things to get that to happen. What you will have to do depends on which QlikView client you have for your QlikView users. Is it IE Plug-in or the full-browser Ajax?