When you order a pizza delivery in the United States, and you ask how long it will take, you get an answer. This answer is almost *always* "30 minutes." Is it really ever 30 minutes? Not in my experience. After a while, you don't believe that answer. So, you either figure it will take what it takes, or you get angry each time the pizza is late (and if it's also cold, well, look out!).
The pizza maker's pat answer is an estimate. You could say it is what it would take if all went well. It reflects a *desire* to provide your pizza in a reasonable amount of time.
We don't really have a way to quickly and easily express that concept in English. You can surround the "it will be ready in 30 minutes" with other phrases, but that would probably frustrate the United States customer even more.
The Spanish language, used where I live in Costa Rica, *does* have a mechanism to express this uncertainty. And, because the pace of life is so uncertain, it is used often. If the pizza is hoped to be there in 30 minutes, the speaker will use the subjunctive. You, the pizza consumer will (basically subconsciously) hear this uncertainty, and will not "count on" seeing that pizza in the near future. You will relax with a glass of Chianti. If, however, you are really hungry, and don't care for wine (whaaa?!?!?), you could then ask the pizza guy, using the indicative, "so, will the pizza be here in 30 minutes?" At this point, the pizza guy will probably answer in the indicative as well - what people from the United States would call "the truth." Pizza guy will think about all the other pizzas in the queue, the traffic situation, the state of the delivery guy's moto, and tell you that ahhh, well, the pizza "will be there in 45 minutes." He might also think about the fact that you seem *really* hungry, and tell you "3o minutes" - but he will also bump your pizza up the queue to make a little more certain you get it then.
If you are fairly new to the language, you aren't as likely to catch that nuance. You will probably be angry a lot.
Interestingly, if you are a native Spanish speaker, you also aren't likely to realize what is happening. You simply absorb what is conveyed via the subjunctive and the indicative. Both answers are "the truth," but mean quite different things - you have different expectations from each answer.