Time's up
I have to say that Tomsmoto has a point to a certain degree. For a complete out of box build where I strip the bike down to a frame and headset cups and then reassemble with appropriate grease and threadlock compound, de - stress, tension and true the wheels, grease the hubs and lube the freehub, seat the cables and housing, adjust the shifting, and adjust the brakes it takes me around 90 minutes unless there is something grossly wrong with a part of the bike.
To compare that to a complete assembly from separate parts that include assembled wheels and bled brakes, it isn't unreasonable to suggest an extra 15-30 minutes to chase and face the frame, press the headset and cut cables. This gives me an estimate of around 105-120 minutes to assemble a bike from scratch. (Some might suggest that there is no disassembly involved in the complete build so I should cut some time from that estimate to compensate, but I find the gross volume of packaging takes its toll on the time clock in a similar fashion.)
If the build involves unbled brakes there is another 30-60 minutes to run lines and bleed the brakes. If there are wheels to assemble from spokes, hubs and rims there is another 60 minutes per wheel. If it is a full suspension frame that I am unfamiliar with I will spend an extra 15-30 minutes with the shock off testing cable routing for the rear derailleur to minimize ghost shifting. If something is not functioning properly and it has been supplied by my shop then I won't charge for any extra time I spend but, if the customer has purchased it elsewhere I will contact them to let them know it is not working and give them the option of paying me to fix it or returning it to the point of purchase. This may not end up increasing the billed time, but it can dramatically impact the delivery time. These factors can quickly increase a two hour build to five hours.
As a general rule the shops that I have worked at have provided a tentative 3 hour build estimate unless there are wheels to build in which case the estimate would be 5 hours. This gives some time to test ride the bike, double check critical fasteners with a torque wrench, and also provides an opportunity to say, "your bike went together beautifully so we only have to charge you for two hours" instead of saying "Your bike was horrible, it took an extra two hours to build."