Unless a sharing protocol is in effect (as with many Asian places) the food should absolutely emerge simultaneously. The point of not going to dinner alone is to eat with someone, not to watch them eat or vice versa. If plates do not come out all at once, politeness dictates that those served not start until those not served get theirs, which makes things awkward and allows hot food to cool and/or congeal. Serving entrees at different times is a sign of a bad or at least chaotic kitchen.