I played around with bag seed, germing, before i purchased good seeds. I had some that turned black, they never sprouted, even 2 weeks later. The easiest way to paper towel germ is to soak them in a small cup of water for ~24hrs, or until they sink, give them a good swirl ever once in a while when they are in the cup. When they are ready, they will be on the bottom, and you will see some particulate matter from the seeds in the water. Then put them on the paper towel. 1-3 days, they will pop. That works 100% with viable seeds for me. I had one of my papaya seeds do just that, turned black, never sprouted.
I also never used TAP water either.
IMO, soaking them will take about 2-3 days off the germ process.