Cross-Platform Timesheet App

I already have a working Excel timesheet containing dropdowns for our job and item codes. What I need now is a straightforward mobile app that mirrors that sheet, runs on both iPhone/iPad and Android devices, and lets staff complete and submit their weekly timesheets directly from the app—no emailing or file uploads required.

Functionally, each employee should:
• open the app, pick the relevant week,
• enter their start and finish times for each day,
• choose the Job Code, Item Code, add a brief description, and record the hours,
• tap “Submit” so the data flows straight to our office for payroll.

On my side, I must be able to update or add new codes whenever projects change without pushing a new build; a simple web console or the ability to import an updated CSV/Excel list would be perfect. The app should also retain all the conveniences of the current spreadsheet: dropdown selections, automatic hour totals, and a clean, familiar layout.

Ideal deliverables
• Android APK + iOS TestFlight build ready for employee rollout
• Source code (React Native, Flutter, Power Apps—open to suggestions)
• Simple admin guide showing how to update the code lists and access submitted data

If you have experience turning Excel sheets into intuitive cross-platform apps and can keep future maintenance simple for a non-technical admin, I’d love to hear how you would tackle this.