1 Handshake block time is = 10 minutes, which is the average amount of time it takes to mine the next Handshake block. That being said, in reality it's more likely for blocks to be mined in less than 10 minutes because a block that takes particularly long would need to be balanced by many "fast" blocks. For example if we assume "fast" blocks take 9 minutes to mine (in reality it's totally random), a single "slow" block that takes 1 hour to mine would need to be balanced by fifty "fast" blocks to average out to 10 minutes.