Automatic Calculation of a Subsequent Time Based on User Input in Adobe Acrobat Form

I am dealing with a form where one is required to enter a specific event time, and another related field automatically calculates a subsequent time point, which is a certain number of hours later. The concrete example of this would be a medical scenario where the arrival time for an appointment is entered, and a "cease consumption" time is automatically generated, being a specified number of hours post arrival time. For instance, if the entered arrival time is 5:30 PM and one needs to halt consumption 2.5 hours post arrival, the form should automatically compute and populate the "cease consumption" field with 8:00 PM. I have encountered several similar questions, yet there are nuances that prevent me from simply adapting the calculation script to fit my case.