No installation is needed. Just open EasyEDA in your browser, register and log in (it's free). Use the Pro edition. Instead of starting from scratch, search for Robert Feranec and open the Custom Keyboard project. Save it under a new name, e.g., "clock".

Rename the project and schematic to "clock". Open the schematic page, clean unnecessary parts from the original project, and rename key elements. Keep only what's relevant for the clock project. Save your work often.

Use addressable LEDs for the 7-segment display. Add, copy, and paste LEDs into the schematic. Rename net names (e.g., LED11, LED12...) so they are clear in PCB layout later. Add LEDs for dots and AM/PM indicators as well.

Insert a header for optional external LEDs. Find the part on the LCSC website and copy its part number into EasyEDA. Add power, ground, and input connections. Mark this component as "NF" (Not Fitted) and remove it from the BOM.

Add level translators to interface 3.3V microcontroller with 5V LEDs. Connect them to appropriate GPIO pins (e.g., GPIO18, GPIO28). Rename nets accordingly and update schematic labels.

Add a buzzer and place it on a second schematic page. Use a passive 9mm buzzer with supporting components: resistor, diode (e.g., 1N4148), transistor, and optional capacitor (marked NF). Make sure to include ports for cross-page net connections.

Place three tactile switches for user input. Use standard push buttons (e.g., with various heights for enclosures). Rename them to User Button 1, 2, and 3, and connect them to GPIO pins 13, 14, and 15.

Use a light-dependent resistor (LDR) and create a voltage divider. Add a parallel capacitor (marked NF). Add a note explaining the light sensor will be moved to the top of the board after manufacturing. Connect to an ADC pin on the microcontroller.

Add an RTC chip with built-in oscillator. Connect power, ground, and I2C lines (with optional external pull-ups). Add battery backup using a low-profile CR battery holder. Add 1 Hz output connection and label VBAT. Mark components on top layer as "NF" for cheaper manufacturing.

Replace right-angle USB connector with a vertical one. Edit the symbol in EasyEDA library editor to match pinout. Save and reinsert the new version into the schematic.