See if you can identify triggers other than time.
If you can find a trigger, eliminate it.
Amp up activity during the day to encourage fatigue at night.
Waken the person relatively early in the day.
When agitation begins, offer a soothing snack.
If dinner is served late, make sure the person has a snack so as not to become overly hungry.
Try placing a full-spectrum fluorescent lamp a few feet from the person for a few hours.
Reassure with calming music, a hand massage, or a favorite TV program.
Hide your own anxiety at this time of day.
Secure the exits with motion sensors, locks, or gates to prevent nighttime wandering out of the house.