The Hill Sphere also changes over time as stars pass us. The galaxy is more of a soup - the stars in the neighborhood don't have a static position to one another.
...so I would imagine that anything even 1ly out would be unstable, over several hundred million years. Solar systems may even exchange very outer outer "planets".
Comments
This limit is called the Hill Sphere: https://en.wikipedia.org/wiki/Hill_sphere
For the Sun it's a bit more than 1 light year, but in practice almost all orbits will be quite a bit under this: less than 0.8 ly.
The Hill Sphere also changes over time as stars pass us. The galaxy is more of a soup - the stars in the neighborhood don't have a static position to one another.
...so I would imagine that anything even 1ly out would be unstable, over several hundred million years. Solar systems may even exchange very outer outer "planets".