The rule of thumb in translucent media is to work from light to dark. This is because working from dark to light has a couple issues: The light pigments can tint the dark areas, and putting light over dark risks smearing and feathering the dark areas and bleeding into the light areas. This is a real risk with media like watercolor paint, which doesn't cure and is always water-soluble unless fixed, or nitro, where each wet coat dissolves the coat under it -- not a risk with poly finishes which lie flat on top of each other.
With a sunburst though, in a sense you're trying to optimize smearing and feathering. In a controlled manner, of course. And you might want the light colors in the middle tinting the dark color along the edge. So, yeah, echoing all of the above: Try both approaches on scrap wood and see which you prefer.