Add time button

Sometimes i am creating a ticket after i have already started work on the problem. Not ideal I know, but it happens. It happens enough that i would really like to be able to put in the time i started working on the problem and then hit the now choice and then hit a "Add time" or start tracking time button that continues to update the "now" or "end" field. that way i dont have to remember to hit that now button when i am done and hit the save button.