I am a Grubhub delivery driver. The wait that you are experiencing when receiving your food really depends on the restaurant. Sometimes they are swamped and tell us it isn't ready yet and that we should come to pick up the order. I waited over 40mins once to pick up a customers order. So by the time I delivered it on the other side of Brooklyn the customers are already pissed off.
Another thing is Grubhub is a shady company. They keep the tips for themselves and don't give it to the delivery drivers. I beg customers not to tip through the Grubhub website/delivery app. We never get that money. Cash deliveries are better for us. Grubhub has conjured up a ridiculous contract and in fine print robs the delivery driver of their tips.