As you say, this is something of an ambiguous question. I believe in all honesty, though, that even if we knew everything there was to know about your app, the best answer we can give is “maybe.”
The process a mobile app designer or developer goes through is generally very similar to the process desktop and web app designers go through. The biggest difference is the constraints that they face, which can cause particular problems when considering developing for compatibility between many different devices and screen sizes. Usually one of the first things decided is what range of devices will be supported, allowing the design and dev team to get a foothold to begin the rest of the rest of the climb towards a finished process.
The next steps will be to define what milestones you’ll need to work towards, and what you’ll need to design and develop and reach those. This is important as the very nature of our business is that nothing is ever truly done, but merely exists in a supremely usable state at any particular moment. In an Agile environment, having established those goals, your team will develop features, user stories, and tasks over the course of the Agile planning process to help you get there.
If you have good developers and designers who are familiar with the constraints of these cross-device compatibility issues, then the process from this point isn’t much different from normal. You’ll follow your teams development organization method (likely some variety of Agile) with a goal of having passed certain milestones by 12/31.
As you can see, a lot of the team’s success or failure is going to depend not on your ability as a UI/UX professional, but on the efficiency of the planning, development and QA processes going on elsewhere in your group. Even the best designers in the world face dependencies that they can’t control. What we as design professionals can control is how we manage and execute our deliverables, hopefully in a way that makes it easy for others in the process to keep the ball rolling.