Mark, have a look at Magic lantern (
http://www.magiclantern.fm/index.html ).
It's easy to install and remove and works with the 6D. I use it on my 600D without problems, and some gratitude for allowing me to have an interval timer now built in.
Check the Software manual to see if it will do what you want (
http://wiki.magiclantern.fm/userguide ).
Trev