My maps take me much too long for the price I charge.
When I'm working at the pixel level in GIMP to remove every trace of white along the border of a client's logo so that no white shows up against the color background it can take me over an hour just on this task.
It's a bit of an obsession for me and possibly not healthy.
For me, the map is the tangible deliverable to the client and I just can't live with something that I'm not completely proud of. Many of them have the map blown up onto a poster board for display at packet pick-up and race day and this really highlights the level of detailed effort that I put into it. Much the same as Toni Youngman stated, it's a creative outlet for me.
It's really not a difference between 5K or marathon that dictates the time it takes. It's more about the detail of the area being covered. Shortest time - 3-4 hours, Longest 8+