I have nevertheless an idea for you, the simple pic16F628 can work as a very good clock by itself, check Elapsed_Timer in the forum, if you are thinking on DS to keep time even when the device is off power then you can consider using the pic in low power too and using the same battery to keep him alive.

Note: you can use even less power with the pic using a 32Khz cristal really convinient if you want to measure time also

If you insist in RTC there is not much more to say than the example and the datasheet. Using RTC is a simple i2C read or write BUT take into account that data is delivered and stored in BCD.

good luck