The ratio between propagation delay and block interval Is there a certain website or a study that gives an estimation for the 
ratio f = Propagation Delay/Block Interval for the Bitcoin network ?
I know the Block Interval is roughly 10 minutes however, I don't know the propagation delay. I define it as the time it takes for all nodes to hear  about a mined block after it's been broadcast.
As mentioned by Ethan Heilman here:


  According the paper 'Information propagation in the bitcoin network.' by Decker and Wattenhofer. The mean time for a node to see a block is 12.6 seconds, after 40 seconds 95% of the nodes have seen that block.




From my personal experience as a developer, this delay is real and noticeable. Some block explorers catch transactions ~20-30 seconds before others. It may be scary at first but its normal.