If it takes longer, you might wonder when it's appropriate to inquire or even leave. Here are some practical recommendations:
If you are not greeted or acknowledged at all within the first 5 to 10 minutes, it's usually not a good sign. Generally, this means that the place is either completely overcrowded or poorly organized. In this case, it might be sensible to get up and look for another restaurant.
If your ordered food takes excessively long and you do not receive a clear answer upon asking, you are not obligated to wait indefinitely. Kindly inform the staff that you unfortunately have to leave – of course, on the condition that you pay for what has already been served to you.