I'm interested in this from the other angle: what antihistamine can I
take at bedtime for relief of allergies, with the assurance that its
sedative effect will have completely worn off by the next morning, but
preferably with the anti-allergy effect lasting longer?

I'm thinking mainly of OTC products. Which has the least duration of
sedative action: Benadryl, Chlor-Trimeton, or what?
Note that I'm asking about duration, not intensity.