Generally speaking, I run two miles a day six days a week. I do the first mile at an 8 minute pace and the second mile at about a 7:20 pace. My average completion time is 15 minutes and anywhere from 15 to 40 seconds.
It's a good warmup.
Today I ran one mile fast because I wanted more time for lifting. Unfortunately it took me like 10 minutes to recover from the one fast mile, so all that extra time was wasted just walking around wheezing.