When should you worry about curling, cupping, or otherwise strangely behaving leaf tips? When it affects the entire plant.
If funny leaf symptoms are present on just one leaf, relax.
But if it covers the entire plant, put on your detective hat and start sleuthing!
Leaves that curl up can be an indicator of drought, while leaves that curl down typically do so in response to excess nitrogen.
Completely cupped or "taco" leaves can be an indicator of a hemp russet mite infestation.
To avoid aggravating the issue with a misdiagnosis, make sure that you're confident of the root cause of the problem before trying to remedy the situation.
If one leaf looks funny, it's probably ok. If all leaves show the same symptom, it's time to worry!