From the support tickets correspondence screen, click on the Add Reply link.
You will now see a textbox where you can write your reply to the client and beneath that, a question that says ‘How much time needs adding to this ticket?‘
In the box below that question, type the number of minutes that you just spent on this reply.
Click the Submit reply button.
You will now see this time has been added to the ‘Time spent on this‘ metric at the top of the correspondence screen.