This might be helpful, it has most of the different striking patterns that have been used but I can’t find any info on a pre hour warning, I wonder if the clock has been set up incorrectly and it is striking on the warn?
This is quite common when someone does not know how to set up the wheels when putting the movement back together. If you look at the movement you will see in the strike train a wheel with a steel star attached to it that lifts a little lever which in turn makes the hammer rise and fall. This wheel should be set up so the little lever sits between two spikes of the star, if it has been set up badly the little lever will be resting on the tip of a star spike so as the strike goes into warn it allows the hammer to just trip over the spike and thus register one strike around 5 minutes before the hour. I could however be completely wrong!