The wording here can be confused with Immediate Dentures, where your natural teeth are extracted and dentures which have been previously fabricated are seated.

Denture in a day means exactly what it sounds like; You come in the morning, records are taken, a wax try in is made, and the final product is delivered the same day, or early the next morning. 

Save yourself valuable travel time and money and get the entire service done in one trip.