Be able to change the timer to Days/Hours/minutes instead of Hours/Minutes/seconds

When I start a session, I'm on for about 5 days and I want to make a history over these 5 days with "Days/Hour/minute" timer so that I know if I've been on Facebook for 2 days instead for 48 hours, looks way simpler to me.
But I won't make it much more than that, because weeks is gonna end up being a math problem.