- "blink" your led
- decide on a clock and learn to drive it -> send to serial (blinking led as well)
- decide on a display + keypad and learn how to drive them (it)-> now to display (blinking led as well)
- debounce those keypresses AND keep things moving on the display (use rtc -> display -> blinking led as well)
- single I2C temperature reading-> display -> blinking led as well
- multiple I2C temperature reading -> display -> blinking led as well
- Triggering of events for making something happen (clock time, temperature, keypad, state machine etc) -> blinking led as well
You're going to have to figure physical drive for your led's - this is probably going to be your biggest issue!
Are you going to PWM drive your LED's to start them off dim so that they are effectively 0 at 7am and maybe 15 at 7:30 then start your 2nd column @ 0 ramping to 15 while your 1st row ramps from 15 to 30 etc etc? if so, sin(x); is your friend for this!
You might also want to think about full spectrum rather than just blue and white (red/green/uv/ir)