Preservation of knowledge: Where are you going to keep it? How are you going to mutate it? Societies are based on information sharing.
Humans have external information transferal systems in the form of writing. If we want to remember something, we have to write it down. If we want someone else to know something, we must either tell them in person or write it down. Given the tens of years required to get a human from their ABCs to the level of astrophysics or David Foster Wallace's Infinite Jest, it seems unlikely that any degree of external information transferal would suffice. They would need something else:
DNA would work nicely as a storage system. It's incredibly information dense, storing billions of gigabytes (exabytes) in a single gram. For comparison, the combined storage capacity of Google, Facebook, Microsoft and Amazon are in the realm of <10 exabytes. Information density of this magnitude is sufficient to model/store everything that humanity knows about the world. Also, the human genome is only about 1.5GB of data.
Let's give the aliens the ability to transfer memories between themselves while they are living instead of just through procreation as life on earth does. This lets them share racial memories as well as whatever information they have gained in their life and want to share. Since ideas are coded in DNA strands, this gives new meaning to "ideas are a virus". Storing information in DNA also means that a single individual could possibly know everything that the species knows. That boggles my mind.
I can imagine how DNA of these creatures is stored as a biological analog of GitHub. If the description of the biology of our aliens is co-mingled with the racial memories, there's an opportunity and mechanism for some super crazy fast evolution of these aliens.
Basically, these aliens would be biological computers of the highest order. If you've ever heard of Turing Machines, that's exactly what these are. But this is just the long(er) term/racial memories. DNA lends itself very well to copying and manipulation but it doesn't fair too well for making fast decisions, so let's give these aliens "normal" brains for short-term memory and immediate information processing.
Time to adulthood: Humans, except in rare cases, don't usually make non-physical labor contributions to society until adulthood. Given that the life-spans of our aliens are so short, let us assume a superprecocial species based on laying eggs/hatching with a gestation time equal to the life span. Being superpercocial basically eliminates the need for childhood. This is beneficial in a few ways. 1) Adults no longer need to spend their short, precious life training/raising young. 2) New members of the species are able to make instant contributions. Also, being superpercocial combined with such a short life span means that whatever form the alien is born in, that's what it's going to look like for the rest of its life.
Gestation: Mammals don't have superprecocial offspring but birds and insects do, so let's look to them for examples of how gestation would work. Birds lay hard eggs that offer protection for the embryo, a nice feature. Insects lay soft eggs or build/find spaces that the embryo can develop in (see honey bee gestation for more details). Laying hard eggs as large as an adult doesn't make any sense as ostrich eggs are only 1 to 4% of an adult female. Let's go with the incubation chamber approach as this will keep adult reproductive organs small and give the aliens a good start on spatial reasoning. An efficient means of feeding a growing embryo would be to include the body of a deceased alien in the chamber when the egg is laid. This gets us a large fat/protein/mineral/water source that the alien community didn't have to gather. And, if the DNA racial memories are stored in a special organ, then the growing embryo can absorb that information to bootstrap their knowledge base.
Energy requirements for breeding:
Let's assume human sized aliens because that's easier to work with. What If makes a good estimation that an average human is worth about 110,000 calories. Let's go with 100,000 calories for simplicity, composed of 62 percent water, 16 percent fat, 16 percent protein, 6 percent minerals, and less than 1 percent carbohydrate. This translates to roughly 16 pounds of fat and 16 pounds of protein in an adult alien. Organizing all that fat, minerals and protein into an adult takes lots of energy on top of just living. Notice that the calorie requirments for human teens is 200 to 400 calories per day higher than an adult but in our case, that development from egg to adult is compressed into a few days/weeks of gestation in the egg. I have no idea how to calculate the calorie requirements but make the point that a human child consumes hundreds, if not thousands of pounds of food during childhood. Whatever it is these aliens eat, they're going to be extremely hungry when they hatch.
Perhaps instead of using fats to power growth to adulthood, the aliens used hydrocarbons like gasoline. Fat gets you 9 calories per gram, gasoline gets you 36 calories per gram. If they can't consume hydrocarbons then they're going to need to live in a tropical jungle because I don't know of any other environment that generates as much life/food. Or, they can form some kind of symbiotic relationship with a another life form that generates huge quantities of food to feed their society.
Gas powered, biological Turning machines. These things are awesome!