That burger joint owner needs to think about what they are doing. As a comparison, McDonald's has 2000 customers a day. The local joint makes $270,000 per year being open 12 hours a day, while chains like Chic-Fil-a make nearly $3M per year. 

100 burgers in 8 hours is 12 burgers an hour. Sounds like this place cooks one burger at a time, 5 minutes each, with one cook, and then the two servers alternate bringing out a burger, so deliver 1 burger every 10 minutes. There may be some room for efficiency improvement here!