Sperm's lifespan. It takes around 10 weeks for the sperm to reach maturity. Once the sperm is inside the woman's body it can live up to 5 days or even longer under favorable conditions. However, when it is outside the body, it can only survive from few minutes to several hours.
The UX developer role is a discipline under the overall user experience umbrella. This means that to become a UX developer you need to have at least a general understanding of the core UX principles, philosophies, and methodologies.
Depending on the scale and style of your project, you might use several of these aspects or not use any at all: User stories. A user story is a short description, discussed with users and other stakeholders, of an aspect of the system's behavior that will be delivered in one of the project's iterations.