The problem with Spider and combos is that what you see now might be completely different in 2 weeks 2 months or a year from now, it's not clean cut like physical deformities that you know will not get better.
A change in temperature can make a difference, I have even seen an animal being ship that was a serious wobbler getting to destination and barely showing any signs (the opposite is true too).
Because it's bad now does not mean it will be forever just like an animal that is fine now does not mean it won't get worse, it's really hard to predict.
Now if the animal fail to thrive and eat on it's own that is where you have an issue and the question is the same regardless of the mutation "how long do you force feed, assist the animal for before giving up?"