=1 / (86400/Last 100 Blocks avg time (s))*(Your Hash rate (MH/s)/NET Hash rate (MH/s))
For me, (3600 MH/s) 1 block take 9,24 day long
= 1 / (86400/278,2)*(10332468/3600) = 9,24
I know, but I want to calculate how long to solve a block from the difficulty specifically, not nethashrate.