fwiw, i find that the fitter i get, the longer it takes me to warm up. given that 8 miles = <30 minutes, that's a pretty typical warm up, no?
also, you dont provide any information about what you're actually doing for training in terms of volume, intensity, what is a "quick" group ride, how long are the hills you're repeating, what do you mean by "intervals".
just based on the tone of your question, i suspect you're new to riding, racing, training for racing, and are making typical noob errors. these typically are solo rides have lots of tempo or terrain based intensity riding that are too easy for real improvement but too hard to sustain and do your other workouts at optimal intensity, that your other stuff has lots of anaerobic work capacity intensity followed by low active recovery intensity/coasting. the big gap in that method of training is that you arent really doing anything that can sustainably develop your aerobic capacity (or functional threshold power).
oh, to answer your question, i really doubt overtrained, but rather under-rested. it's really hard to over train. it's not very hard to under rest.
You seem to have me pinned. And I think I am just under rested as you say. I have a lot of late nights as a college kid...I just started hill repeats/intervals and do approx 1-2 min of REALLY hard efforts followed by 3 min recovery and I do them until fail pretty much. But before this my "hard" rides were 1-2 hours long. But in reality my "hard" rides and recovery rides were pretty much similiar in overall effort. I need to pick up a book on this. Need to wait to get paid though.
Also I have definitally found that my "warm-up" period has increased. I needed a full half hour before I felt good enough start hitting the repeats last week at 100%, but my heartrate didnt shoot through the roof like it did saturday when I was getting warm.