Final answer:
Perishable foods like hot subs should be kept at a safe temperature, and it is recommended to prepare them as close to the pickup time as possible.
Step-by-step explanation:
The amount of time in advance that a hot sub can be prepared depends on the temperature at which it is being stored and the desired quality of the food. According to food safety guidelines, perishable foods like hot subs should be kept at a temperature above 60 degrees Celsius (140 degrees Fahrenheit) to prevent bacterial growth. If the hot sub is stored in a properly functioning hot holding unit, it can be prepared a few hours in advance as long as it remains at a safe temperature. However, it is recommended to prepare hot subs as close to the pickup time as possible to ensure maximum freshness and quality.