1. Design:
Design the 3D model of your Ben 10 watch using 3D modeling software such as Blender, TinkerCAD, or Fusion 360. Be sure to include spaces for electronic components, watch movement and 3D printing mechanisms.

2. 3D printing of components:
Divide your design into separate printable components (case, bracelet, etc.). Use a 3D printer to make these components using suitable materials, such as PLA. Be sure to get precise details and a high quality finish.

3. Electronic:
Integrate electronic components, including an Arduino board, OLED display, buttons and battery, into the 3D printed enclosure. Connect the components to ensure proper operation of the system.

4. Programming:
Program the Arduino board to manage watch features, such as time display, date, and other specific Ben 10 features that you want to include.

5. Assembly:
Assemble all electronic components into the 3D printed enclosure, making sure to secure connections and ensure proper integration.

6. Test:
Run tests to ensure all components work together. Also check battery life.

7. Finishing:
Make sure the assembly is clean and all components are secure. You can also add finishing details or customize the exterior appearance.