There isn’t a simple single-number rule like the 500 rule for this. The amount of drift depends on more than focal length alone, including your sensor size/field of view and how much movement you’re willing to tolerate in the final stack.

In practice, stars move more than many people expect, especially with longer lenses. A better approach is to calculate sky rotation/drift for your specific setup and decide your own acceptable limit in pixels, degrees, or image area lost at the edges.

One community answer recommends using a dedicated star-trail/drift calculator that estimates movement for a given lens, sensor, and time, including trail length in pixels or millimeters. That’s more useful than trying to rely on a rough rule.

So the answer is: no widely used equivalent of the 500 rule exists for “number of frames before resetting.” Use a calculator for your camera/lens combination, test how much drift your stacking workflow tolerates, and expect to reframe more often as focal length increases. If you want much longer runs without reframing, a star tracker is the real solution.