Is it ok to take nyquil after a nebulizer treatment? or how long should i wait in between the two types of medication?

Maybe/not. You don't mention why you do a nebulizer treatment, but Nyquil and similar products contain a sedating anti-histamine as its main active ingredient. Antihistamines in that class can thicken mucus secretions and most docs discourage their use in asthmatics. If this product does not seem to affect you in a negative way it may be okay to use. Timing would be of little importance.

Continue your usual asthma medications and your asthma action plan for an increase in symptoms, which may require more frequent treatments. The NyQuil may be substituted for nasal saline rinses, topical vase rub and humidified air. Avoid cough preparations if possible. Drink warm soothing fluids with honey to soothe your throat and lessen irritation. Watch for fever. shortness of breath.