Based on all engineering assessments; the solar panel installation plan, area on rooftop, height elation if any, and other design parameters are approved.
Based on the design, the installer shall be able to give a final quote. The varying charge section can be defined with tentative time the setup shall take to get installed. On approval, they provide for the list of documents you would have to submit for the entire process.
You can get your final quote and schedule of the solar installation process. You can decide to stick to your service provider, negotiate or switch it based on your experience of the process.
This entire process takes in account the experience of both, the engineer and the solar installation vendor. Thus, it can take a day to one week for your design approval and quote finalisation process.