There are numerous factors that affect how long a vehicle will take.
The two big ones are the size of vehicle and quality of your clientele.
Don't underestimate how long a jeep or a suburban will take compared to a Kia Rio. Charge more for big vehicles and a little extra time is no big deal. For example, on interiors: I charge $90+ for small cars but $150+ for tank size suburbans.
Your clientele is also a HUGE factor. If your prices are fairly low (and they will be naturally as you are getting started) and you're marketing heavily on craigslist and to dealers. You'll be getting some extremely difficult, candy corn and melted gummy worm cars.
Everybody starts here, with these super hard junkyard cars. There is no way around it. It's grueling, hard work but you will learn a ton.
Also, don't underestimate how long even a good one step polish will take. Beware, a full, true paint correction can take 2 days +. Don't listen to guys that say otherwise. Charge accordingly.
The answer to your question: I spend about 3-6 hours on the average, full detail, without polishing. So no, 5-6 hours is not too long.
I can hear your desperation even in your short post. I could be wrong, but I'd bet that you are getting burned out from not charging enough. If you aren't charging enough, 5 to 6 hours is a long hard day. If you are charging $30+ per hour, it doesn't seem so hard any more haha.