Never be afraid to program in an extra day of rest if you feel your body needs it. Don't be a slave to any training schedule, this one or any other. Having said that, if you take too many days off you will compromise your training program.
Balance is essential in any program for success.
You don't want to do too much, and you don't want to do too little. Today's scheduled workout is to run an easy 3 miles followed by strength training. With six weeks behind you, you now have completed half of this 12-week Spring Training program. One reason I schedule changes in distance is for variety, so you won't be running the same distances day after day after week after week. It's a mind thing.