Project timeline is a combination of resources & scope. As humans we want more in less time while paying less for it which doesn’t really work so need to compromise on some of the asks. As engineers the best way to solve the above is to address it mathematically with good estimates for each component of the work and then assigning resources to the work thereby estimating time needed to finish the work. This is followed typically by a series of negotiations with stake holders to compromise on scope and increase time or resources.
Generally, my approach is to get a minimal viable product out as soon as possible and then iteratively make it better. Reason for this approach is that users don’t typically need everything they want and once they have a minimal product, they can better understand which resources are more important to them. Secondly a product needs to go through several iterations before its technical design solidifies. We as engineers can thus learn from our mistakes in design and adapt to changing user preferences on following iterations. Thereby doing iterations on the minimal viable product enables better design choices than making an attempt to have a solid design out in the first iteration.
However, clearly communicating this strategy to stakeholders and senior leadership is essential so that expectations are clear and budget for successive iterations exists.