That is such an open question dependent on so many variables - client demands, designer speed/quality, printer etc - that I think anything from 3 days to six months for each one would be a good time estimate.
Depends on complexity of the project and workload at the time. I have done t-shirt art that took 30 minutes and I have done t-shirt art that took 20 hours or more total. I like to have more than one project going at a time for monetary reasons so it would depend on what I have going on at that time as to how the time for the project is spread out. I find that rarely do I sit down and do a job start to finish without jumping around to different projects.
Some of the answers you got are a little sarcastic due to the fact that it really is a question that can't be answered without a lot of additional information. Much in the same way as if you had posted questions like these?
• How long does it take to build a house?
• How long does it take to draw something?
• How much time does it take to drive somewhere?
If you provide more info, we'll try and answer as best as we can.
The reason I was asking is that my co-workers don't seem to understand that Graphic Design is actually something that requires at least a little actual drawing and visual acquity etc.. The act as though it is typing and should be almost instantanously. I will never forget having a 15 Page coloring book assignment, A website and a stack of other projects given to me on Wednesday afternoon and everyone expected there projects to get done by the end of the week and they actually have some kind of quality... I am the only graphic designer where I work and it gets very very very busy sometimes...