Is allegra (fexofenadine) 24 hr safe to take everyday for a short period of time (one month or so)?

Yes. Allegra (fexofenadine hcl) is generally safe to take everyday, provided it is taken as directed. It should only be used for as long as needed (ie, during allergy season / allergy symptoms). Allegra-d however, contains a decongestant, which can cause palpitations, insomnia, elevated blood pressure and other stimulant like effects, and is contraindicated in some patients, ie, hypertensives.