Yeah, 3 hours should be long enough. I've never done it before and a friend told me how. So, I tackled it myself and finished in 3 hours 45 minutes. So, an experienced mechanic should get it done in that time or less.
I just replaced mine, used this valve spring tool>Deluxe Universal Overhead Valve Spring Compressor
KD 3271 $44.75
Made the passenger side a breeze due to the handle comes off and used a 5/8 wrench on the last 2 springs, Great investment and took a first timer about 2.5 hrs.