How long does it take for nyquil to kick in?

Nyquil is not prescribed as a sedative and should not be taken as such. While it has been known to make one drowsy it does not affect everyone in the same way and may not have the desired effect even if you were to take in excess of the recommended dosage. I would not encourage you to use Nyquil for this purpose. There are other medications that you can take that will help you sleep. Talk to a drug store pharmacist for advice.