How to estimate the time to create an app?

Hey,

I work in a team where only I know how to develop a frontend. My team supports various departments within the company.

I gave a proposal for a frontend application and delivered that within a week. It is fairly complex two page application with

1) Editable grids 2) Multi user support. The changes made by one person should be immediately reflected for others. 3) Realtime monitoring dashboard for various events via rest api. 4) Authentication via cognito 5) Deployment of frontend and rest apis on kubernetes. 6) Testing using cypress.

Now my manager doesn’t have any experience with frontend and think it is a baby’s work.

He expects me now to deliver additional similar realtime app within two days. It also have similar requirements.

How should I explain my manager and this is not a couple of buttons, tables and charts and there is actual solid amount of code that goes into it?