Find answers to frequently asked questions about the different ZYRTEC® allergy products, as well as information about indoor and outdoor allergies. Questions about: ZYRTEC; ZYRTEC Dissolve Tabs; ZYRTEC-D; Children's ZYRTEC; General Allergy Questions What's the best time of day to take ZYRTEC®. Any time ZYRTEC · ZYRTEC Dissolve Tabs · ZYRTEC-D. But I was wondering whether timing matters. Is there a particular time of day that's best for giving him his allergy medication.