Detemine total time taken by a group of processors?

[#1]

What is most convenient way of determining total time taken by a group of consecutive processors?

Do I need to log time before first  and after last processor, and then take the diff?

Or there is some inbuild feature that can help me on this?

[#2]

This served my purpose.

${now():toNumber():minus(${lineageStartDate}):format("HH:mm:‌​ss", "GMT")}

I added it to a LogMessage processor, and I can see the result in logs, though sending it over a mail would be terrific.

[#3]

@manishg 
Why not use the PutEmail processor if you want receive this information via email?
The "Message" property in the putEmail processor supports NiFi Expression Language, so your EL could be used directly in this processor as well.

Matt