This is what I do when I have guests. I let them take a seat while I order my meal without the fries, which, more often than not, are suggested by the cashier. Then I pay for my order. I start timing. I tell the cashier that I have more orders for my guest/guests and I pay for them separately. Then I ask my guest to get some peanuts and drinks with cups provided, while I get ketchup or vinegar in front of the counter where I observe how many times the fries are shaken, the cleanliness of the kitchen, etc.
When my order comes, I note down the time in my head and if the crew was smiling or friendly. The rest of the order, I do not time. I check carefully my order and after I have eaten a few fries, I visit the washroom. My guests check their orders too but that is not going in my report so I let them handle it.
For the sum of expenses, I total both orders. I add the tip I placed on the box. Then for my order, I already have the lone receipt with a sandwich, fries and a drink, which is the only one scanned and timed. Done!