Add a small amount of water and polishing powder to the mirror, place the mirror on top of the tool  and start to polish slowly and smoothly using a w stroke of 1/3 the amplitude of the mirror diameter, listen for any unusual noises if heard stop straight away and clean off the mirror. It is possible a small piece of grit has been trapped that may scratch the mirror

Completely polishing a 6 inch mirror by hand can take more than 8 hours! I have found that breaking the polishing time into 2 hour sessions works well.
It takes about 1 hour of polishing for the tool and pitch to warm up properly, if polishing is going well there is a firm but smooth resistance to the mirror as it is pushed across the lap.