Best simple structure: one saved employee list, then workers only use two big buttons: Check In and Check Out. Time and date are taken automatically from the phone.
Best workflow: 1) choose employee, 2) type site if needed, 3) tap Check In, 4) take photo, 5) later tap Check Out, 6) take photo again, 7) app calculates total hours automatically.
Best for workers: very simple screen, big buttons, no manual time typing, and required photo proof at entry and exit.
Best upgrade later: add GPS location, Google Sheet backup, and salary calculation.