I just finished an oil change minutes ago with about 7k miles on the oil and the oil was coal black (which is typical). I don't have to worry about the time since my truck gets driven on a daily basis.
Also changed the air filter with about ~32k miles on it.
Just a side note my last oil change was with Delo 10W30 to see if I could measure an improved fuel economy over the Shell Rotella 5W40 I've been using to date. What I found was there was no fuel economy change so I went back to the 5W40.