Time. The importance of the Reddit algorithm, over all other algorithms, is time. When a user submits a post to a subreddit the clock is ticking. The first five minutes of a post are the most important five minutes of the posts history. Upon submission, the post will show up on the subreddit’s /new section. During the first few minutes, the most loyal and devout Redditors will decide to upvote or downvote the submission. There is also the opportunity to comment on the submission. Note that comments were not part of the early days of Reddit.
Within the first five minutes, the Reddit algorithm calculates and places a value on the number of upvotes, downvotes and comments. Oftentimes, comments are even more important than upvotes because it can send the post to the subreddit’s /controversial page. Downvotes destroy the chance for the post to advance to the /rising or /hot section of the subreddit. If a post does not gather enough momentum to get to the /rising section of a subreddit it is going to be buried and will garner no attention.
If a post gains momentum in the first five to 10 minutes, it will show up on the /rising section of the subreddit. This is where the momentum really takes off. If it is truly a great piece of content, Redditors will upvote and comment giving the post the power to get to the front page of a specific subreddit. This can take anywhere from 15 minutes to an hour.
Remember, time is of the essence with the Reddit algorithm. If the post takes an hour or more to get to the front page of the subreddit, it has little to no chance to get to the actual Front Page of the Internet (Reddit). If a post gains steam rather quickly, it will move up the page on the subreddit and could show up on the Front Page of the Internet.
Users will not see the total score (upvotes vs downvotes) of a post until it is one hour old. Sometimes, users will see very hot posts get to the front page of Reddit in under an hour which is why there is no score beside the post. This is rare and usually only happens with major news or an extremely popular post. The Obama AMA comes to mind. Breaking news also gets to the front page of Reddit rather quickly.
What the Reddit algorithm offers that Facebook, Twitter and even Google do not is the importance of time. If a piece of content is popular, it will start as popular.
In the early years of Reddit, there was great debate from users about potentially gaming the system. If a college student was sitting in their dorm room, they could submit a post to a subreddit, message all their friends to go upvote it and have a very strong possibility of getting to the front page. Reddit figured this out quickly and devalued the important of upvotes and comments from the same or similar IP addresses. One would imagine they have parameters in place to devalue upvotes and comments coming from users logged in in the same vicinity.