Issue with Flight Gear while integrating Simulink and Flight Gear

Hi,

I am working on a visual flight analysis system for drones using Matlab and FG. The idea is to take a flight log and visually see how the vehicle flew using FG. I have successfully integrated FG with Simulink. However, once I start running FG, day and night starts rapidly changing. It obviously takes some duration of time as day, and night. I have specified the time of day, time zone, etc, in BAT file. I have played with Simulation Rate and Time Warp. None has helped. I am using FG 3.1 and Matlab R2015a. And, the input data to Simulink is in the form of a structure.

Any suggestion/idea on debugging this issue?

Thanks.