We think you did not get the idea.
RTC must be powered (by coin cell) to keep time you have set.
For instance, if today you upload and run a code witch have RTC.setTime("12:06:06:04:08:45"); and then you turn it off, when you turn it tomorrow, same time will be set because same code line will be executed.
To avoid that, you can run one time RTC Setting and Reading Time Example
with your current time, and then upload your code with no more changes on RTC. Now you can switch off your waspmote and turn it on next day, time will be right.
Hope this helps.