What is the best way to build a fantastic user experience in the shortest amount of time?
You could ask a hundred UX designers and not get the same answer. While there are methods to guide you to success in design, there is no formula that promises a good solution.
When you are working on a new product, speed is very often an important factor. Investors or stakeholders want to break even or become profitable, as quickly as possible to stop the bleeding of money on a new project.
Many software and web development teams utilise the Agile process as their project management framework of choice to accommodate this quick speed.
https://usabilitygeek.com/ux-mvp-agile/