A rule of thumb is to multiply the rendertime of the first pass with something between 300 and 400. this depends on the complexity of your scene and the "noise level" of your textures. If you do that you have the rendertime without AA. It takes some experiece to make a nice quess on how much extra time you need to add to get the rendertime with AA. If you're already rendering on fine-art mode you shoud multiply the rendertime of the first pass with 500 to get a realistic rendertime. Usually for medium AA intensive scenes the AA pass takes about 1,75 times as long as the last pass before the AA pass. I've become better in quessing rendertimes than bryce. These are the rules of thumb I use, but you need to get some experience to get detailed enough to beat bryce.

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