Few changes to above answer:
Edit armbianEnv.txt by
sudo nano /boot/armbianEnv.txt
And append i2c0 instead of i2c
overlays=... i2c0
install i2c-tools
sudo apt install i2c-tools
If your "sudo i2cdetect -y 0" returns 68, run the following commands first:
Load rtc-ds1307 by
sudo modprobe rtc-ds1307
sudo echo ds1307 0x68 > /sys/class/i2c-adapter/i2c-0/new_device