Some companies that offer search engine submission claim they can guarantee listings on Google within as little as 24 or 48 hours. How can they do this?
You have to read very carefully what's being offered. It's impossible for anyone, or any company, to guarantee when or how quickly your website will be crawled by Google and added to their index. Any company that claims they have some special tool, or relationship with Google, that the guarantee is based on is flat out lying.
Other companies offer to get you traffic from Google within 24 hours. That's something quite different. They are talking about PPC (Pay Per Click) advertising using Google Adwords. This practice is frankly deceitful and dishonest, unless they confess they are talking about PPC. Unfortunately, most play tricks with the words they use claiming "you won't be asked to pay any Pay-Per-Click charges". All this means is that they are paying for the ad servings out of your subscription to their so called service. You might also find that the traffic you get is actually them clicking on the ads they've placed.
PPC is a good thing, and proves highly successful for a great many websites. But it has nothing to do with search engine submission, or the natural search results - organic listings.