if you are climbing a steep section, you might go 1.5 miles a hour. if you are cruising along on flats or easy downhill, you will go 3 miles per hour. if you've got 7 hours of hiking time, you'll easily do your 12+ miles every day. no need to rush in the high sierra!
i don' schedule my breaks too much when i'm hiking. just try to get going early, get some good miles done before lunch, take a long (or really long!) break/nap, and do some more after. take breaks at water, passes, pretty spots, etc.