When the client and DCS-5020L are both located on the same network (i.e. same LAN), the throughput will be significantly greater than remote access, where the client and DCS-5020L are on different networks.
For example, accessing a DCS-5020L using mydlink from within the same LAN will have near real-time responsiveness for pan/tilt functionality. Accessing the same DCS-5020L from another network will result in a lag of at least ~4+ seconds for pan/tilt functionality. The lag will vary (and can be as much as ~9 seconds) depending on a variety of factors.
This is considered normal performance for these cameras.