It’s always helpful for your server to have as much information as possible when you’re dining out, as it helps them ensure you have the best experience possible, within their power. Dietary restrictions? Let them know so they can alert the kitchen staff. Not drinking alcohol right now? Allow your server to make a recommendation for great non-alcohol alternatives. The same goes for time. If you’re short on time, it’s always good to give them a heads up. Just make sure you do so politely.
If you’re in a rush, most servers will do their best to ensure you are out of the restaurant when you need to be. But there may be some things that are out of their control, especially when it comes to what’s happening in the kitchen or behind the bar. At a crowded restaurant or drinking establishment, it’s rare that the server can leapfrog your orders over those of other guests, so don’t take your frustration out on them if the food and drink don’t come out as quickly as you need them to.
Where telling the server you’re in a rush can turn rude is when you are also unwilling to adapt. Don’t say you’re in a rush if you’re dining with a large party. Or, place a full order of appetizer, entree, and dessert. Give the entire order at the same time and request to pay when the order is placed. These are all things you can do to ensure you are able to leave as quickly as possible. Finally, if you notice the place is truly slammed, instead of staying and becoming frustrated that you need to cut your meal short in order to get out of there, leave and find another place. That’s why fast-casual restaurants exist.