the extended stats are more complex than that. For example, a get on a remote key, you access the time() like 4 times: before start processing command, before send the ClusterGet, after send the ClusterGet, after processing the command (command execution time and RTT+Remote Execution time). 

It is easier for me to have a duration method. I don't wanna waste more time check for each stat, how many times the time() is invoked to calculate the duration :(