If your technigue of "adjusting the clock" is based upon receiving the keystroke and then directly manipulating the register in the RTC chip....then I would instead do all the editing into RAM locations and then program all of the locations to the clock at one time. If the clock supports a "stop" bit it is wise to set this bit into the STOP state when writing the new clock values. (Some RTCs have a special bit in a status register that indicates when the internal clock circuits/microcode is trying to update the RTC. If you have this make sure to heed its indications of when it is legitimate to access the RTC).

With regard to BCD format RTCs. I almost always convert to and from binary format register by register as I read or write the RTC. This way I can keep the internal S/M/H D/M/Y information in the program in binary format which is much more convenient to work with using the native microcontroller instruction set.

Michael Karas

PS.
Have Fun.....If your RTC application goes beyond one of just showing Date/Time and requires a certain amount of "date arithmetic" then let me know. I can show you algorithms that can support something similar to Julian Dates (Day number since a reference time) that will work through this next century.
MJK