I've been using this library for months, I must never have tried an alarm on Saturday. Did you change the macro for day of week?
#define dayOfWeek(time) ((( time / SECS_PER_DAY + 4) % DAYS_PER_WEEK)+1) // 1 = Sunday
This one did give me fits for a while before I found it in an old post. And, you did know that the library returns the identifier for the alarm and that can be checked in the callback to see if it's the one you want. That identifier can be used for other stuff also.