I'll address the specifics above and some of the other points in the thread as well

1. Expectations are the responsiblity of the person who has them, not the person who is fulfilling them. Expectations of an employee need to be coupled properly with the tools, training and feedback needed to fulfill them.
2. "Key points that help..." There needs to be a written list of assembly standards, not some general "ignore ___, just make sure..." On the other hand I find assembly checklists to be silly - a check-mark is no guarantee that an item was done at all, let alone properly. The service manager should insure that every assembly can be tracked to the assembler and that random checks are done.
3. "Just get everything bolted down..." will not sell the bike as well as everything working well and a consistent, clean appearance.
4. "The 3 month period...the squeaky wheel..". You are making the customer responsible for finding problems instead of the shop for preventing them. In 3 months a too-tight rear wheel bearing can be ruined.
5. The time an assembly "should" take is primarily under the control of the service manager by means of the specific assembly criteria, tools and resources, training and employee selection/retention.

As others have pointed out it is impossible to give even a reasonable range of time for an assembly - too many variations due to style of bike, quality, assembly standards in general, and shop facilities, assembler responsibilities (dedicated to assemblies or subject to interruptions for flats, 30 day checks, etc).

That being said I would not find it credible for one to expect all of the components of a proper assembly to take less than 40 minutes per bike. The reason becomes apparent when one looks at the tasks involved in an assembly, which extend far beyond "put together and adjust." Here is an quick example:

[TABLE="width: 337"]
[TR]
[TD]TASK
[/TD]
[TD]TIME
[/TD]
[/TR]
[TR]
[TD]retrieval of the crated bike
[/TD]
[TD="align: right"]2
[/TD]
[/TR]
[TR]
[TD]uncrating/unwrapping bike/components
[/TD]
[TD="align: right"]5
[/TD]
[/TR]
[TR]
[TD]full lubrication/adustment/check of all items
[/TD]
[TD][/TD]
[/TR]
[TR]
[TD]shift
[/TD]
[TD="align: right"]4
[/TD]
[/TR]
[TR]
[TD]brake
[/TD]
[TD="align: right"]5
[/TD]
[/TR]
[TR]
[TD]bearing (rear wheel removal required)
[/TD]
[TD="align: right"]4
[/TD]
[/TR]
[TR]
[TD]and attached component items
[/TD]
[TD="align: right"]3
[/TD]
[/TR]
[TR]
[TD]wheel truing
[/TD]
[TD="align: right"]5
[/TD]
[/TR]
[TR]
[TD]inflation
[/TD]
[TD="align: right"]1
[/TD]
[/TR]
[TR]
[TD]wipe down
[/TD]
[TD="align: right"]2
[/TD]
[/TR]
[TR]
[TD]disposal of box/ packing
[/TD]
[TD="align: right"]2
[/TD]
[/TR]
[TR]
[TD]moving the bike to floor or storage
[/TD]
[TD="align: right"]2
[/TD]
[/TR]
[TR]
[TD]completing paperwork
[/TD]
[TD="align: right"]2
[/TD]
[/TR]
[TR]
[TD]and restoring the work area
[/TD]
[TD="align: right"]2
[/TD]
[/TR]
[TR]
[TD][/TD]
[TD="align: right"]39
[/TD]
[/TR]
[/TABLE]

The list is one I just dashed off and the times off-the-cuff as well, and is assuming a typical front wheel, pedals, seat/post and handlebar unmounted boxed 12-24 speed bike, with handlebar already lever equipped. Some shops may prefer a short test ride, more extensive paperwork (labeling/signage, update of computerized inventory, etc.). And of course this is time for a dedicated assembly without interruptions. Any task that requires multiple interdependent steps will suffer at least a significant interruption penalty if one has to break rhythm and concentration to do something else. "Let's see, where was I, where is that tool..."