Defining the project schedule
You should have at least a rough idea of how much time you'll be spending on the project. The phases should be split to:
Plan
Design
Make
Test
Deploy and refine
Power Apps is intended for rapid development. However, many factors affect how long it can take for an app to be completed:
The experience level of the person making the app
Whether you're using an existing app as a starting point for design or implementation (this will speed things up)
The number of apps to be created (for example, our expense report process will require one app for expense report creators and another app for the approvers)
The number and complexity of the features your app needs
The type and number of data sources to connect to, and whether you need to collaborate with other teams to get access to the data
The availability of project participants
As your plans and scope become more clear, you can refine your schedule estimates.
One way to shorten development time while maintaining (and even enhancing) quality is to use an existing app as a template. Whether you're using a template provide with Power Apps or Power Automate, another app developed in your organization, or an example you found elsewhere, templates and reference designs can help with screen design, interactions, and data architecture.