60 hours usually obviously depending on complexity and number of frames.
I have used this technique in earlier versions of SolidWorks where you had less control over the render able time frame. There was a command to reverse the animation so I set up two computers, on rendering forward and one rendering backward. Another thing you will find is that saving directly to .avi can be quite annoying. If, for instance your render crashes, the whole avi is destroyed. You can save the animation out as a series of numbered .bmp frames, this way even if the render crashes you will still be able to start back up right where the system went down. There are a lot of applications that can take these image files and convert them to a video file. QuickTime Pro, Flash, and 3Ds Max are some, I am sure there are other open source ones as well.