You've touched upon a subject that is very important to me. But first let me comment on something you said in your post. The general gist of it was that you are creating a 3d model from your 2d design. It is my opinion that this approach is exactly backwards from a more efficient approach of creating the 2d details (or layouts, etc) from the 3d model. How did I form this opinion? Hopefully It will become evident.
So, to your main theme, you are interested in determining a method whereby you can estimate more accurately the amount of time it takes to produce a drawing (or design, or project).
First and foremost, do you know accurately how much time it had previously taken to produce a particular drawing? You must establish a benchmark, and really a very gross estimate isn't good enough.
Next, do you know how long it takes you to produce a particular type of drawing? Do you know how long it takes Hans Johnson. to produce a similar drawing? Do you know if your efficiency is greater or less than his? Are the drawings in question worked on by both you and him? Is one producer 's final drawing a higher quality than the other and conforms to the standards in place?
If you do not know the answers to these (and many more) question then you need to put into place the means to begin answering them. You need to begin monitoring, logging and examining the logs. You might want to start by trying my CadTempo software http://www.cadtempo.com for a 30 day trial.
Ok, how did I form my opinion about going from 3d to 2d? hopefully my departure from your question will help answer some of your other questions.
I started my business 20 years ago. Prior to that I had been doing the same type of work on the drawing board and had kept meticulous records of my time involvement. I do machine design and each machine will have a number of compontents whether they are designed, detailed, and manufactured or are commercially available. By knowing the component count I could determine how long an average machine of xxx component type took to design or "layout", then detail, then check.
During start up I decided to do all my work in AutoCAD because it was highly customizable and also offered AutoLISP as a programming language. I discovered that AutoCAD's TIME command was essentially useless. When you save one drawing into another name the time would carry along. Also if you left a drawing open the timer would just keep ticking along. Not a very good way of determining how much time it took to produce a drawing. So the first order was to create a lisp program that would track my time more accurately.
I learned it took longer to produce a design than manually drafting did, much of it having to do with the learning curve. After some menu tweaking, some custom lisps etc the time came down to a little less than board drafting. I knew I could get it down further so I set a goal for myself and began determining what needed to be done. Looking at my logs I could determine if things appeared out of the ordinary from my previous experience. And it occurred to me. Why am I drafting most everything six times??? Yep, that's right six times - during layout: front, top, side...during detail: front top side. Why not draw it once in 3d then extract the drawings and views as needed.
Any long term AutoCAD user knows that the earlier releases of AutoCAD did not lend themselves to convenient 3d work so I had to create some 3d lisp routines and menus and macros to speed things up. It worked! My design and detail time started improving dramatically, I'll not bore you with details but I continued to improve my methods and techniques and a lot of different things. Every change resulted in moving my time up (bad, so let's not do that) or down (good, ok maybe I can do that even better).
It is not a task to be taken lightly, it takes persistence and determination to arrive at your goal but it starts out by benchmarking.
We design in 2D first since it takes fewer time than drawing in 3D at first.
Clients require a specific timeline for presentation of General Arrangement 2D Drawings.
In any case, you have made an important point here.
We use AutoCAD for 2D and Tekla Xsteel for 3D. But most probably we can use Tekla for 2D design as well... I am not sure if we are using the AutoCAD 2D finished drawings to import to the 3D model and start from there, so I will have to check.
Thank you for your posts...