Having worked in bike shops for a number of years (i would not be happy if the builder of my bike took less than 2 1/2 hours to build it up (not including wheel build) lets take a typical full suss:
face bb (properly) 15 mins to 30 mins (some frames are terrible!)
ream (or just check reaming) on seat tube so not to scratch new seat post 10 mins
Cut steerer of fork to length, fit crown race taper steerer tube and fit fangled 30 – 40 mins
face disc mounts front and rear (if your fitting kings to fox this’ll take ages) 20 – 40 mins
Set up and bleed brakes (45 mins minimum)just puttin discs on wheels properly takes 10 minutes!
actually put whole lot together, set up suspension for riders weight, dial in gears, re-adjust brakes is necessary etc….. oh i give up, anyway it takes a while if you want it done properly.
Also take into account cabling, putting on end crimps, paying an outagious fee to dispose of the huge amount of packaging that came with the parts.