As @dynamicgreentk mentioned, a little goes a long way and it’s easy to over-do neem treatments. Oils can clog stomata, but if used in the correct ratio then you’ll be just fine. Also only applying when it’s not too hot or cold and the sun isn’t directly beating down.

It makes no sense though that it would leave a carcinogenic residue two weeks before harvest but no other time. From my understanding, Neem oil is completely safe. The only reason you don’t put it on before harvest is because then your flowers end up with a very strange off putting peanut butter taste. Far as I’m aware that is.

On the contrary, a quick search reveals neem oil as being a cancer preventative: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4734358/