Your data draws pretty fast for me, so I'm not sure if it is your connection. I also adjusted the playback speed to the fastest. The map does clear the data before drawing the next time interval. There's not much we can do here because the browser is drawing the data.
Some things I can suggest...
Can you draw the different polygon in different colors? This may help with the visual differentiation between different times. Drawing with the same color blue doesn't really highlight the differences.
For possibly increased performance, you might generalize your data. Your polygon has over 8000 vertices, and hundreds of "rings" or holes where the land is. The server basically returns all of this data to the browser to draw.
Hope this helps,
Mike