cjcj: I also did buy the DS3231 AT24C32 clock... I did however write code in a sketch to run my clock - and I was so proud of doing it. Is it better I use this module? Isn't that sort of cheating and relying on pre made components!
Why get a dog and bark yourself? The RTC module has several important advantages over using the Arduino as a clock. It will be much more accurate over long term, Arduino will probably loose/gain several mintues per day, vs several minutes per year with ds3231. RTC has battery back-up, so doesn't need re-setting every time Arduino is powered up/reset.
cjcj: I'll order the shift registers, mock up 15 small led displays with it, then write the code to learn how to do it.
Make sure to buy common-anode individual/single-digit 7-seg displays for your mock-up. You won't be able to use multi-digit displays without multiplexing them, and that wouldn't be an accurate mock-up of your final curcuit.
cjcj: Below for instance is an example of the code I've written for a MM:SS timer. You'll look at it and think it's quite long winded. But self taught, so far it's the best I can do.
Its good that you are practising your coding skills, but little of that code will be suitable for your project. You won't be multiplexing, you will be using shift registers and an RTC connected to the i2c bus. For now, better to spend your time getting the code for that RTC module working. Just send the output to serial monitor for now.