It seems that average Peercoin blocktime is about 8min instead of 10min. Any explanation?
It’s a well understood behavior, though difficult to succinctly explain.
“Peercoin PoW block generation is coupled to PoS block generation as well as PoW hash power and is therefore difficult to approximate, but the total block time of Peercoin can be empirically estimated to be around 8.5 minutes.”
Block difficulty is just an estimate of how long it will take a for a block to get solved. It can come faster or slower, but always averages around to that 8.5 minute mark for Peercoin. Classically, Bitcoin around 10. Just an estimate with a moving average to keep difficulty in check to maintain this window.
Thanks. I was trying to see if peercoin has a more stable blocktime because I thought there would be no big miner switching on and off big hashing power at will, shocking network difficulty, while big POS minters have more limitations to do the same. It looks like the miners for ppc POW blocks can disrupt blocktime, too.
As @thehuntergames showed, PoS difficulty (or more precisely, the number of PoS blocks between PoW blocks) affects the PoW target. So it really is quite complex.