There are several other threads for using the RTC. Basically, you write one patch to set the time, then you can use the RTC nodes for reading the time in other patches. You should only need to set time on the RTC once (or you might have to reset it occasionally if it is not very accurate, or change it for daylight saving time if that is important for you).
In your case, you could pick a day off week and hour/min to run your cycle. If the cycle will take longer than one minute to run and you code it so that it doesn’t check clock while cycle is running, you should be ok. Otherwise you could run into problems where it tries to run multiple times during that minute, or if you check for specific hour/minute/second, there is a chance you would miss the second if processor was busy with other things. There are times you need to be careful about checking for exactly equal, but you should be ok if you only need to check day of week, hour, and minute.