Hello
Im also making a software RTC clock with a LCD and a 3-button user interface and im very soon finished. With my program i can set one start time and one stopp time. When the software clock is equal to the start time a port pin is going low and when the clock reaches the stop time the pin goes high again.

Is this somthing similar to what you are planning to do?

In that case i can send you my code in C