Final answer:
The boxed lunches should be discarded by 12:30 p.m. if they are not eaten.
Step-by-step explanation:
According to food safety guidelines, perishable foods that are kept at a temperature between 5°C (41°F) and 22°C (70°F) for more than two hours should be discarded.
In this case, the boxed lunches of roast turkey sandwiches and coleslaw were refrigerated at 5°C (41°F) prior to being set outside for service. As long as the food temperature does not exceed 22°C (70°F), the lunches should be discarded if they are not eaten within two hours of being set outside, which would be 12:30 p.m.