This is going to sound a bit weird, but I had some schedules which were slated to start at 10pm. They kept having issues and was running about 2 to 3 minutes late. I corrected it by moving the time back to 9:59pm.
you may want to try that and see if it helps. I did a test over the course of days to determine what the settings should be. Here is the forum / topic area I discussed this: Scheduled Rules