Time Steps

While simulating our case, we have used strict time step with maximum as 1800 seconds. But still, it is taking a time step of 0.1 sometimes. This is making our simulation quite slow during the middle of simulation. As per our observation, we found the process of simulation with good time steps at the beginning but it is taking smaller steps as the simulation is going on.

Is there any way to maintain standard time steps throughout the simulation process??